If the catcher drops or misses the ball then any borderline pitch should be called a ball. When a catcher muffs the catch of a pitch it is awfully tough to call a borderline pitch a strike. It is another illusion. Everyone thinks that the catcher missed it because it was a ball. Good coaches expect you to call this pitch a ball.
Good coaches expect their catchers to squeeze it.
If the catcher muffs the catch call it a ball. If the catcher catches it at his head-height or above it's too high. The catcher's head should always be used to help you find the top of the zone. Anytime a catcher must reach even slightly above his head everyone believes this to be too high despite what the rule book says. This guideline obviously relies on the catcher's size.