A couple of clarifications may need to be made. I do not shoot "everything" premounted. My comments on straight grip guns referred to heavy loads, and the guns they are used in are duck guns and pigeon guns. I wouldn't know how to begin to go about shooting a duck premounted. Doves, either. Quail either. I premount for sporting clays and flyers, but not for FITASC (obviously). So, you are laboring under a misconception ("I don't shoot like you do"), about how I shoot. Certainly, we may not shoot alike, probably don't, but it's not because I premount for everything.
However, I fail to see how premounting has anything to do with what takes place upon the shell firing. Everyone is premounted before slapping the trigger, unless they're shooting from the hip. A premounted gun, as well, is nicely "tucked into my shoulder pocket", as you say.
Interesting that you get no gun movement upon firing. Do you shoot many 1 1/4 to 1 5/8 oz. loads out of straight gripped guns? That was the point of the first part of my post.
Thanks for the comments..........SRH