If in your Aikido you class this as part of irimi then fair enough, thus I may understand how some may be using the term so thanks for that. However, for me I would never use irimi to mean staying on line.
Would this movement
be irimi in your eyes?
入る - i ru: It means to go in/into, to get in, to enter, to break into
身 - mi: body, one's place, one's position
Yes true, we always use irimi to describe "going into" aite. Even when leaving the line and letting aite pass through not this is called irimi but maybe tori nuke or something like that. irimi is the coming back, the stepping in onto aite or his place.
Irimi nage (at us!) is called this way because for throwing we step into and through aite. (As shown in the video.) It is not called irimi nage because of the iniating steps. If we throw directly it maybe called irimi nage omote. If we let aite pass through and turn around it maybe called irimi nage ura.
Here examples of tori nuke
, letting aite pass through. Even if sensei sometimes gets behind aite I wouldn't call this or think of this as irimi.