Look at Chris Mcrea and Romantovich who anchored our Pan Am team. He jumps every fence high-headed and flat-backed. Not much release required, and he is clearly not restricted jumping a foot over the top of FEI heights.
There are plenty of horses that jump flat with little change in their head/neck position. 3'6 is small to them and they politely step over it. As the fences get bigger (i.e jr/ao jumper level) they may use their body more, hence the releases you see. But at 3'6, not necessary.
I owned one like this. It was just how he jumped, and no amount of gymnastics or generous releases changed that. I sold him for some nice $$$$ as an eq horse.
You seriously have no idea what you are talking about.