Grip with your calves and your lower leg will stay in place
It’s not really about the distance, I rarely miss one, and it’s something that I do even on smaller and bigger jumps together! I’ve posted the sequence of a vertical on my profile if you have the patience to take a look I would be grateful
As a tip u can always grab mane over the jump if you are afraid of catching the horse in the mouth. I think maybe part of the reason why you sit too deep in the saddle and pull on the reins is because you get left behind. This can happen when you take a jump too long. That's why u practice finding a distance to jumps.