you do have to maintain control of the gun regardless. Slipping is not an option. Though position guns are much more so set up that you can run the hand to the handstop generally, than my service rifle rules allow.
You do not wnat to transmit pulse or other movement though too. I have a bad pulse in my neck and in my stomach that I Have to protect against. The stomach one is related to other than standing and I cannot constrict it or it will bounce the gun. The neck one simply is keep the neck off the butt and all will be good.
The rubber is no different too than whats on your shooting pants and jacket.
We used to always use shooters sticky spray too, so that while we were sweating like a pig, you still could make sure nothing slipped as you were firing or in strings of rapid and so on due to recoil often. As you note smallbore isn't a recoil or rapid fire issue though.
