I'm going to throw out and old timer's thoughts on this. I have been studying firearms since I started mowing lawns at age 12 to earn the money to buy gun magazines. That would have been about 1972.
I have come to the conclusion that some things "just are".
That is to say, despite all the numbers you can crunch, they don't explain everything. For years it was thought, that when both were driven at full throttle with factory ammo, the .41 magnum was a bit faster than the .44 magnum, but most gunwriters felt it was less accurate. A funny thing happened when reloaders too to it. They went with different bullet weights and even committed the unthinkable---they loaded it at les than max velocity!!! They loaded it with 210 -220 gn bullets at around 1,2000 fps and found that its accuracy became impressive. Indeed the tightest 20yd group I ever fired with a new to me handgun was with a Ruger Blackhawk .41 just so loaded.
If that load sounds somewhat familiar it should to 10mm shooters. It is in the ballpark of thee 10mm, especially if you do a little juggling for .401 v .410 .
On top of that there is the platform we are discussing. I admit to being completely unimpressed with the accuracy of the Glock 9mms that have crossed my path, I am not saying that the accuracy is terrible at all, but I have always had at least one or two other 9mms that have been more accurate, and I am talking about service autos.
My G-22c is the least accurate of the four .40 cals I own. Not terrible accuracy at all but simply not as accurate.
So we come to the G-20 SF. Not any special modification to the basic Glock Design, just on a bit different scale for the cartridge. Yet, my G-20 I markedly more accurate than the G-22 and is right in there with those accurate 9mm and .40s I have, not just with most of them, but with the best of them. Same holds for my .45s. and couple of them commanded a premium because they were built FOR accuracy. SO how can this be? I don't use the word "surprising" in terms of accuracy, I think it is overused, I prefer "unexpected". So why is the G-20 delivering it?
I think there are factors, as my Dad used to say, "that don't fit on a slide rule". For all I know it might have to do with "the frame flex in that frame size works to create the perfect harmonic effect with the wall thickness of the 10mm barrel" It could be that the velocity of the slide divided by the mass of the slide multiplied by the weight of the recoil spring (in grams) when divided by the square root of the muzzle energy, yields a magic number known to be divine among the ancient Mayans and, by some ethereal coincidence the Tibetan Buddhists .
On the other hand, maybe some thing just are.