OK ... I feel compelled to offer a situation and see if anyone has additional device.
I think that for better or worse ... this can happen to anyone ...
Caver with a standard rack is caving with someone whose rope is 1/2 dirty. I'm picturing the clean 1/2 of the rope is rigged on bottom 1/2 of pitch and dirty part is on top half of pitch. Now ... person is using ON-ROPE approach and feeding rack from close distance.
Friction changes dramatically on rope 1/2 way down and caver pinches finger into rack because feeding from 12 inches or 8 inches away from rack. Caver lets go. Not sure this ever happened to me. But I am sure I've been on rope many many times when friction changes dramatically.
Also fairly sure I have been glad to be applying BUTT-friction at the time. As an eight user ... (shorter pitches) ... I might be recalling an 8 experience. Can't say for use.
Anyways ... I didn't know that proper use of a rack was also license to feed rack from closer and pinch fingers. I'm open minded. Maybe it should be exactly as you describe. I am guilty sometimes of using prob too few bars (4).
Not at all want to get flamed or flame anyone. And I know that we all assume plenty of risk in any approach we take in caving and climbing.
[Edit:] Just found this on a seemingly related site. Seems relevant.
http://caves.org/section/vertical/2012% ... Manual.pdf