Precisely... when most people talk about atemi, they're mostly referring to the initial overt go no sen or sen no sen response... as in... uke attacks, nage responds with a "softening up" atemi, or as uke begins to attack, in the same moment, nage enters with atemi to forestall. Or as some sort of "tacked on" adjunct to the technique - as in... now your body is here and this target is open so you can hit it - without neccessarily considering how a strike to that target may create a different dynamic to the intended technique. Atemi waza is not indiscriminate and must follow a logical progression, in line with the 5 points I listed above, that naturally results in the completion of the technique.
For review, your five points were:
1. A predictable physiological response in uke
2. Disturb/disrupt or even break uke's balance
3. Causes uke to change their priorities and respond in a predictable fashion
4. Create an opening to allow insertion for a technique
5. Allow for completion of the technique
.. but your points are only signs or effects, not causes or methods. I agree that a strike that did not effect one of the above is not proper atemi , or at best an affected atemi. My five points are methodological and for greatest effect -- should all be present in a strike. Having written them down now, they seem to have an unintended Buddhist flavor -- though I doubt Prince Siddhartha would approve of them.
The strike must occur with:
1. Right shape
2. Right placement
3. Right orientation
4. Right speed
5. Right time
You will note the common factor of being "right" which resolves to juji 十字
. I do not mean merely "correct," although that is implicit, I mean "right." As in right angle, 90 degrees, square. That principle flows in dynamics so it is not so trivially seen as in statics. It has elements of both space(ing) and time(ing), and is the reason that distinguishes good maai from bad maai.
One key is resonance. An object reverberates at its natural (or resonant) frequency when struck. Resonance occurs when the object is struck at its resonance frequency. Resonance also occurs when any input is delivered 90 degrees out of phase with some induced frequency (i.e. -- the gross motion of the body). 180 degrees phase difference is collision or 100% negative versus 100% positive); 0 deg or 360 deg (reinforcing or merging --is positive meeting positive and negative meeting negative), 90 degrees phase difference is between them, and harder to characterize.
Right shape is the shape where the forces imposed result from using tangential impacts -- energy at right angles to the radius to the center of some rotation or potential rotation -- not linear action/reaction but a shape that delivers right-angled stresses to the target and sudden torques. Think of the head-snapping upper cut, right cross or left hook as examples.
Right placement is placement on a target that maximizes the degree of right angled stresses propagated in the body of the target. This varies depending on range and dynamic, but because the articulation of all the body parts involves a member swinging from a center, typically you attack not the swinging end of member -- but in relation to a center of that swing and impact. Center of rotation, center of percussion and center of mass each may affect the result of the strike depending on its relation to those points.
Right orientation involves striking the dynamic target; the strike must be oriented at a right angle to the predominant line of travel. In a dynamic target on two legs this line of travel is deceptive, because in moving forward , the body sweeps out an angle of rotation centered on one hip, as does the arms making a strike that one might counter with another strike. Thus, right orientation means that in striking the center of rotation ( or in relation to the center of percussion or mass) you do so at a right angle to the radius of swing at the time of impact.
Right speed is more subtle, because the tendency is to try to deliver more speed as speed incurs more energy into the target -- forgetting that the body can also control absorbtion of energy into parts that are less vulnerable to sudden stress. . So it is more important that the speed used limit the ability of the body to control its absorption of energy. Absolute relative speed at impact may varys with a moving target, but its natural frequency does not. WHEN you hit it the speed of the strike also creates a reaction frequency response in the body of the target -- modulating (damping/absorbing) the initial impulse frequncy down (or up) toward the natural frequency. The target's (human body's) natural or resonance frequency is around 10hz, and when you strike it with an impulse at that frequency, the body's own reverberation adds energy to the striking energy AND it cannot damp it. If you strike it AT that frequency (speed/rhythm) you set up a resonance that allows the energy to "FIND" its way into weak spots in the structure in ways that neither natural frequency damping, nor the voluntary or trained responses of the body are easily able to counter by absorption/redirection into its stronger parts. A glass cracks at resonance because the vibration at the resonance frequency builds up stress that can only be relieved by a structural failure -- at the weakest points of the structure in respect to that stress.
Right time is related to the gross motion of the body and the same 90 degree resonance. The body "rings" at its resonance frequency when struck, but the body obviously can also drive its motion in a much wider variety of speeds or rhythms. Thus, the proper strike must come in time relative to the target's overall motion at a 90 degree phase difference to that motion as well for maximum disruption. This relates to orientation at a deep level, and can be easily seen in speedbag practice where ( if one is doing it effectively), the bag is always struck midway between max and minimum of its swing cycle -- right at the point where it is returning through the 90 degree pendant position. A speed bag is not aiki -- but the prinicple involved is the same. If the speed bag were a striking limb and the swivel the head or body, in aiki you would more likely strike the swivel (center of rotation) or elsewhere (like above or blow the center of percussion) I won't digress into that but look here: http://en.wikipedia.org/wiki/Center_of_percussion
The body is sensitive to this set of resonance problems and has a response to it -- reflex action. When an impact impulse sets up a stress wave that exceeds a certain impulse rate in a certain critical place, the spinal reflexes react by involuntarily extending (or flexing) the limb affected -- losing structural stability (i.,e structural failure), but thus saving the integrity of the structural material (typically , an important joint). Thus, when you apply sankyo at a certain critical rate, uke's tippy-toe reaction (reflex extension) is spontaneous -- above or below that rate and you are just using pain of the torque but at just the right impulse frequency ( same as furitama
or tekubi furi
resonance in your own body) you are literally pressing neurological buttons. When you apply kotegaeshi similarly at the correct impulse rate (even with small amplitude of movement) you get spontaneous knees buckling behavior (reflex flexion). Shihonage similarly -- except that you are in the way of their falling down (briefly).
So this is one way of understanding aikido as 90% atemi, since the controlling waza should be delivered in the same manner, with the same five factors as a impact atemi.