After reading this thread awhile ago I finally got to test my MTC UL I purchased afew Weeks ago.
When I fist set it up it was VERY windy so today I noticed it wasn't set up right, I slackened the locking screw checked the p.o.i & it hadn't changed, altered the p.o.i until I was happy & tightened the locking screw, I checked the p.o.i again & it hadn't changed. It was abit windy today not ideal for zeroing a scope but I didn't notice anything strange with using the locking screw.
I then went on the HFT practice range just for a quick test, I felt the parallax setting needed changing which I did there & then, on going back to the zero range to check if changing the parallax had changed the p.o.i I found it had changed it, again I unlocked the screw & found the p.o.i to be same, adjusted p.o.i again for the new parelax setting & tightened the locking screw, same again didn't notice any change in p.o.i with using the locking screw.
Will hopefully get a nice windless day to get a proper test/zero, although the way the weathers going ill have to find a indoor range for that.