Hi, I had similar issues when I moved a character too fast or through a wall. I found that using larger rigid bodies like the “UE4 FleX rig 2” sample helped. Unfortunately, this would only be useful for rigging and it would lose most of its soft body properties. It also didn’t interact well with cloth and liquid (tends to pass through).
The particle size was also an issue because the size has to be fixed for all interactions (character, clothing, water). It would be cool if it supported variable particle sizes but I guess it wouldn’t work as well on the GPU. I was more interested in testing a full character so I used large particles. As you mentioned, this wouldn’t work well for small details like hands or the face.
Because of this I thought I’d try another approach in code. In the “FleX animated rigid bodies” samples I created the equivalent to an active ragdoll. It only needs particles on the mesh verts and is hollow so I can use smaller particles and keep detailed areas like hands. I was also thinking of using a smaller mesh for the particles (overlap). Cloth and liquid should also work (haven’t tried it yet). It should be possible to stitch objects together with springs e.g belly fat soft body, could bounce off ground from a fall. The main downside is that it doesn’t use the integrated branch so I lose most of the features. Its also very difficult to control (can pin areas but it could cause similar movement issues like attach to rigid). It might be interesting for basic characters like snakes.
Overall I think the first method mentioned in the tutorial would probably only be useful something like cutscenes with slow movements. It would be really cool if the integrated branch included FleX characters one day. It’s a shame that it has these amazing water, softbody and cloth features but you can’t have a character with two way interaction. I doubt it will be added however, as FleX is really only supposed to be used for secondary effects. I’m probably going to be working on some VR projects so I won’t be using FleX for a while.