Question: Is heaven/earth/man a commonly enough and openly enough discussed concept in CIMA that anyone doing an CIMA should be familiar with it on a physical level?
Well, that gets tricky - they may be familiar with their definition of what that principle means, which in reality then does not translate into any demonstrable physical skill. It's like the buzzwords in aikido - someone can say I use "ki" or "kokyu" in a technique, but then it's all externally powered movement with a big exhale at the end.
Strictly speaking, the heaven/earth/man notion of internal strength principles is kind of a classically written in stone thing that many martial artists (including Ueshiba) referenced to show 1) They were in the club with the buzzwords 2) Their skill and practice were in accordance with the buzzwords. (I'm being facetious about the buzzwords, go ahead and insert your own terms - universal principles, laws of reality, physics, yadda yadda). Of course your ability to discern to what level someone's words and skills were in accordance with the buzzwords also depended on your own understanding and achievement in what the buzzwords were describing.