I don't really know how to answer since I haven't seen a definition of IP/IS. I also think that the founder used "Aiki" in wide variety of meanings (e.g. Aiki Budo - a prewar name of his art, Aiki as moving out of the way, Aiki as being solid, etc...) and an attempt to fit that "Aiki" into an "aiki paradigm" seems to me an unnatural one.
One can ask "How important was the 'Tenryu ability' to the founder and in the way he saw his art" - my guess is that not very, but I am nowhere near even trying to prove this.
I started in the '70s with Tohei Sensei coming to our dojo several times a year just to teach a Wednesday night class for the regulars.....one point, relax completely, weight underside, & extend ki were all part of the normal conversation........ The problem was the depth of the detail available to go along with these terms......there wasn't much, not enough to get a real handle on. The same was true of the aiki taiso.......not much detail. We did all of the ki testing.... Got good enough at it to understand how to bypass them and how to kept anyone from really testing at that level. When I asked folks How do you teach, how do train folks to establish one point, relax completely and the others in the face of attacking intend, moving and under stress? ......there was no answer.
After spending a whole lot of years in my waza phase I went back to asking. I started checking folks out, started paying more attention to a few friends who had some answers and looking outside...... I found Dan. Combining Dan's approach with my friend John's stuff I can see value in what I was shown in the 70's.....the keys to useful learning and application. All we got then was hints, now I can see connections.......