To use soft physics without this issue, you could try reducing the fat collider radius outer multiplier or the overall offset in the plugin's Physics tab -> Fat Collider Radius window. Alternatively you could use Collider Editor to reduce the radiuses of adjacent AutoColliders to prevent the fat colliders from bumping into them.
I tried that. Unfortunately the indent still doesn't go away.
However, I think you have discovered the underlying issue being with colliision. I had suspected the same. This issue only seems to occur when I have models in a specific mounting cowgirl pose with the arms close to (but nowhere near touching) the breasts. This pose is ironically the default starting pose I have for a cowgirl scene I have been working on for several months, which is why I encounter this issue so often:
Something about the arms seems to be colliding with the breasts. I noticed the same thing when I picked up
Lilith yesterday. She has indentations even with TittyMagic, Soft Breast Physics,
and Fat Colliders turned off:
Turning off collision looks even worse and and the indentations are still there:
However, even if I turn
everything back on (Collision, Soft Breast Physics, TittyMagic, Fat Colliders) and let the scene progress to a point where her arms aren't squeezing close together with her breasts slightly in front of them, all the issues go away:
The same with Kinx:
So this is clearly some kind of weird collision between the arms and the breasts in the base VAM that is sometimes exacerbated by TittyMagic (in the case of Kinx) but is sometimes there for Looks without anything involved, including collision (in the case of Lilith).
So my ultimate short term solution seems to be just getting those arms further away in the starting poses of the scene. Longterm, it seems something needs to be adjusted with base VAM and the way arms collide with breasts in some Looks.