For what it's worth, pro QB's look at defenders as do receivers. Routes adjust based on the defender's technique for which there are only six. Off head up, Off inside, Off Outside, On head up, On inside, On outside. At all levels of Football, High school to the league, A go, fade, jet, deep sideline, 9 cut which ever terminology you choose should be thrown 45 yards down field 6 yards from the sideline all depending on defenders intial pre and post snap allignment. The decision to throw a mortar pass is made .5 seconds post snap and is actually done at 2.5 seconds from a launching point of approximately 7 yards deep. The depth is attained from a common 5 step drop or gun snap drop both from the same launching point. There are multiple variations of the mortar pass for shorter throws launched from a more shallow depth. The most important rule is the defenders technique and the receivers initial pressing of technique which actually determines what kind throw it should be. All this happens within 2 seconds. The aiming point for the mortar throw is from the head up. The rifle pass is from the head down. Receivers must utilize their body's position to gain advantage based on the defenders technique and position. Sounds complicated but it's really sandlot football which is not played much anymore. A QB should know where his receivers are going, therefore the QB sees holes (zone) or chasing defenders (man). At least that's the way Coach Paul Brown taught it.
The first step to be successful is for receivers to line up correctly. Unfortunately, many very talented receivers line up on the sidelines which forces the QB to throw the ball out of bounds. Coaches yell and scream and blame the QB when in fact not even the greatest could hit a guy 45 yards downfield in a 12 inches radius. So really, we've just discussed only one type of pass. If I insulted your intelligence my apologies, but many high school QB's wind up being Tuba players instead of playing in the NFL at no fault of their own.