Hello. Thank you for comprehensive answer. I made the test that you described. If i understand well red lines represent constraint equation which are connecting nodes that are inside pinball radius region? But they are NOT rigid body elements, right ?
I made some tries with different pinball radius but nothing changing. Why is that ? Please look at the picture below there is no difference between 0,1mm radius and 50mm radius.

The red lines are only visible with MPC formulation. And what about other formulation ? What they are doing with nodes ? If I leave formulation as Program controlled there is no red lines so I assume that MPC formulation is not the default one.