Thanks for you feedback, I’m happy to see you’re playing with these things. Both of these come from quirks in Bullet we’ve been trying to resolve for some time now. The first is a thing called margins, which is padding put around shapes that help keep the simulation stable. We try to offset the shape to hide them but as you can see it’s imperfect. The other is the connections tolerance with physics. They just aren’t as tight as the connections solver when not using physics. I haven’t found the right incantation of settings to make get them where they need to be yet.
It’d be super helpful to see the model though to confirm these are the issues, and try to resolve them.