Good stuff Robson!

seeing your penis base get pulled inside-that is basically activation of the ischiocavernosus,
Which is partly true. The IC's can be engaged in a way where they squezze forward towards the pubic bone and no pull inside happens.
I can engage the 2 IC "legs" towards the back which pulls penis in and forward/"out" where it pulls the penis from it's anchoring point inside "out of the body".
Also the base can get pulled in by a bulbospongiosis kegel too... which creates confusion for people who are not yet aware of the IC.

I think both muscles have better grip/access in different penis positions and states..
(sitting)erect penis pushed to the side and down with hands gives IC easier access against the "weight".
Erect penis pushed up with hands gives BulboS more access to engage against..
That`s cause they work together stabilizing and maintaining an erection together depending on the position. I think cerain sex positions people lose their erection might point to an imbalance or weakness between both muscles.