Just when you think you've got it all figured out... that's when you get a good old kick to the bolloc
That's springer shooting for you
Coming back to the original question of this post though - I don't think it matters too much how you hold the gun, as long as you can do it consistently.
When you're thinking about consistency though, you should also remember that you'll have to adopt a variety of slightly different shooting positions around an FT course. Is your position consistent when you're shooting uphill / downhill etc etc..
It's not good enough to find a position that works brilliantly for you sat on the zero range, it has to work around a course too.
Just to illustrate that, just before the start of the GP series last year I decided I was going to try shooting by resting my hamster on my knee. In practice on the zero range it was mega! felt like I couldn't miss and super stable!.
GP1 comes along and I put down my first target - great I thought, why didn't I think of this sooner. I missed the next 8 targets and couldn't work out if it was wind catching me out or something else?
In desperation I decided to put the hamster back up and go back to my old position (gloved hand bracing front of knee and gun resting on the V between my thumb and fingers).
I started clearing lanes again, but it was a bit too late to rescue my score by that time.