Side plates are loose
I have recently been experimenting with a couple of side plate (bolt catch cover plate) mounted scope mounts (that I've had laying around for years) on an older 185 series mini.
The two I have, one an older B-Square, the other an equally old Ram-Line, both exhibited the same problem. They use a drilled and tapped side plate and machine screw to attach the mount, and two screws that bear on the top of the receiver in a "teeter-totter" arrangement to do the coarse elevation adjustment. In theory, that should work. In reality, the side plates are so undersize that there is a significant amount of play. Not too surprising, as I'm sure this is a non-critical dimension for Ruger. It would be better if the scope mount manufacturers made their side plates a bit oversize, so that users could trim them down. That's probably the same issue as with the UTG mount.
My solution was to shim the sides of the side plate with thin strips of aluminum foil until I could detect no lateral play. I then cut a shim from stainless steel sheet metal (available at your local hardware store or hobby shop), which I attached to the bottom of the side plate with rubber cement to eliminate vertical play.
I also had to make a sheet metal shell deflector, which I attached to the scope mount with pop rivets, after ejecting brass destroyed the first scope I mounted. Spring is here at last, and I hope to finish some other mods and get the combo out to the range for testing in the next few weeks.