The physics of very tall guys shooting is different than that of 6-footers.
The ideal case is a very short person who can barely reach the cylinder but do it every time. The shot will rise to it's max height in a long arc and softly come down on the rim if off a little bit.
For a 7-footer who may be releasing the shot at 9-foot.. if the ball is shot to barely clear the rim it will be very flat and fast. If he introduced a normal 45 degree arc.. it's high point might be.. where? 15 feet? And have 5 feet to travel downward towards the cylinder.. picking up speed.. slightly off.. that clangs the rim fairly hard.
It really is tougher for big guys to hit free throws.. that's why to OP talked about the underhand shot.. it changes the physics.
Myles is a bright guy. Someone explain it to him from a physics angle.