I'm guessing that the reason why the Alien Gear holster closes up a bit and the Stealth operator doesn't is because the stealth operator is all kydex while the Alien Gear is a leather/kydex hybrid holster.
I have several hybrid holsters that I've pretty much stopped using because I just prefer all kydex. My go-to OWB holsters are Blade Tech. My favorite IWB holsters are from PJ Holsters. I also recently got a light-bearing OWB holster from Priority 1, and I am very impressed with it.
That seems to be the case. I was at my local range this morning and talked to a couple of guys who have Alien Gear holsters. They said that theirs work just fine though. It sounds like AG just night have good batches and bad batches. I plan on sending mine back since the Stealth Operator holster worked just fine for me with the drills I was doing.