there's pro's and con's to any demo, since it's basically showing just ONE thing or a couple things out of context (i.e. fighting).
In this case I like to have the guy really lean in and do the push up because many times, especially in a video demo, it can be hard to tell if the demo partner is really even applying force or not, or how much. at least in this case, it's obvious that force is indeed being applied.
i like to move around and show the relaxation because, of course, if you can't change and move than what good is the skill? basically i'm trying to make it a bit more obvious that these skills can actually applied during some kind of real movement.
my thing is that this sort of thing at he very least is not really possible using "arm and shoulder strength" unless maybe you can bench press 800 lbs.
Sorry I haven't had time to look at your video clip until just now. Thanks for posting it. I think it achieves your main aim of showing how "these skills can actually (be) applied during some kind of real movement." You take on the downward load and move with it while staying pretty relaxed--particularly in the shoulders, which for a lot of us (including me) remain a sticking point. Looks like the load is moving right down your spine and through
your hips, which remain loose and adjustable in transferring the load (allowing for kicks, for example). I see where becoming aware of and training the use of the mingmen area comes into play, more clearly with your demo than with most of the taiji push-hands work I've done or seen.
As was noted, the demo clip you posted is different than the sort of "static" (in terms of external movement) standing test that Dan describes, or the Aunkai "push-out" test. In my own partner practice with different static/standing postures, exploring how to most effectively engage the lower spine and supporting tissues (fascial and muscular) is becoming more important with time.
For me the question of fajin,
release of power, seems
qualitatively different than taking on the load of an opponent's weight, or incoming force, and absorbing/neutralizing/returning it. Exploring how the breath can support (or interfere with!) fajin and neutralization is giving me some (very tentative) ideas about deeper internal connections at work with both fajin and neutralization that might bridge that perceived difference. In particular, keeping the breath relatively smooth and continuous and not
locking up the diaphragm under load seems important in these very early stages of learning.
Ark and Dan both often do, to varying degrees, something at the point of contact (with their partners) that felt to me, in different circumstances, like it either drains my force or alternatively impinges into my center--with hardly any overt movement on their part. If there is any "path" at all in their bodies it seems very short. So it may point to the difference between "short" and "long" paths and energies described (with less than stunning clarity) in taiji writings.