I have the same set up as you (V3I and sunray) and the same problem with stubble. I found adjusting the Disc Sensitivity down helped some . I took the sunray off and that help some too.
I don't think detectors are really made for the shock of whacking into things even softly . I switched to using the 6 X 10 and that helped the most regarding getting stuck around stubble and the like. I haven't tried a concentric coil but a solid coil does work better for me than an open one in stubble. Mashing down on the stubble might cause ground balance related falses as well
My Etrac has similar issues when bumping/mashing around. It does seem taking care to hold the coil level parallel as possible to the ground helps as well. (try a slower swing speed).
I have considered making a cordless weed whacker for my other arm out of a old metal detector to cure the problem at the source.
Between the headphones,harness, belt, bag, detector and probe and then add a weed wacker and a pair of bug eyed sunglasses. With the beeping and the whacking, flailing both arms around I would most likely look like a old man creature from a mad max movie. People would move away, probably way away. That might be a plus,
But more seriously I am going to try tightening up everything from one end of the detector to the other both mechanically and electrically to remove what interference I can from shock due to bumping things as a " next. project".
If you can't tell, It has been raining for days...
Happy hunting