It was actually a lcp2 and late lc9s. With pinky extension, the follower would rest visibly and measurably lower. In both cases, ruger sent me additional mags, with the flat bases. Issue was transferable to new mags with the pinky extensions. Mags all worked with flat bases. The negative effect was an occasional failure to lock back, which never occurred with the flat bases.
As I said above, i have had other pinky grips that made it more likely for me to strip the mag on recoil, hitting the mag release and exerting the bit of downward force on the pinky grip. And i suppose with the rugers downward force on the pinky grip could have combined with the lower follower height to prevent lockback. Thus maybe wouldn't appear with another shooter, but the measurable difference, and the contrast with the flat base plates, convinced me it was partially causal.