In ID: 965221 "Allow back passes" there was a request to allow "back passes" (and I do not see a way to add this comment there). That term has been used at JuggleWiki to mean back tosses, and there is a difference. At JuggleWiki back tosses have beeen animated without the figure's elbows passing through the body, by adding intermediate positions going and returning. However, a similar atempt to show back passes for '66111' failed to prevent the "snapping elbow" effect.
My suggestion was to program limitations to where the intersection point of arm lines can be, modelled on what is in fact possible. Turning inside out is not possible, nor is passing through the body area. My notion was to allow negative front-back values only within a realistic range of sideways values.
This is also a problem with showing body rotations for pirouettes, kludged at JuggleWiki by setting additional hand positions at every beat, resulting in a "mechanical" effect with some jerking at start and stop, and not allowing the hand positions raised to the chest as commonly used while turning.