Nothing is going to change, it's what you feel comfortable with. I pinched with two fingers from day one, it just felt right for me, my instructor was a thumbs only guy. I have always felt more comfortable with a neck strap and it's a bit high, above belly. When I don't use a strap I hold the radio low about crotch level. It's a no thought thing, it just happens. I fly with several guys that use a tray. Most of them are older, maybe it's an age thing. Due to neck problems my right hand goes numb after a few minutes of looking up, I may give the tray a try and see if it helps at all. Some writers think the two fingers give better control, others feel the two fingers gives a pull to the right? When I do any vertical stunts I often remove my thumb and pull only with my index finger and concentrate on a straight smooth pull. Whatever works, there is no real answer to the question. Whatever feels correct.