I had an adjustable stripper made for my Ripley as the barrel is with a shroud (AR5s) for a bit of experimenting. Yes I did make a mistake on my measurements and the screw thread needs to be about 15mm longer to put a second locking nut on.
However for my experiments it has done what I needed. For me I set it about 8mm away from the end of the barrel. It moves approx 2mm per complete revolution. I found that it the group sizes did improve as the start of the stripper got closer towards the barrel. From memory mine is about 1.5mm from the barrel.
As a side note the sound of the pellet escaping from the barrel end changes as it got closer to the barrel end. Admittedly I was experimenting in the Autumn and I never had a truely still day to check my results but in the conditions the actual group size did come down.
I may well get another made a bit longer and a few other smaller changes.