very nice
@Gunther. i like your excel file. i still try to figure out how you wrote the text in a diagonal direction
btw, there are more details that should be mentioned according to collision and bodies in box2d (xui2d)
1, if you can, use always simple bodies. at the end, box2d is just a calculation library so as much the body is simple as less calculation it will need. simple bodies (rect, circle)
2, walls, ground, and bodies that should not be moved should be static bodies. you could use kinematic bodies without setting velocity to it BUT static bodies use much fewer calculations. this will make your game using less the processor and make it faster.
3, if you move a body very fast it can happen that no collision is detected so you need to set the body .isbullet property to true but don't do it on each body only on bodies that move very fast.
if i will remember more points i will put them here.