I think it's easier to define tap heights as parallel to the drum, but there's less room for error as far as uniformity goes. If everyones taps are parallel except for one person, it's very noticeable. But it looks sweet when its all perfect!

In my line, I teach the 3in tap height. Like you said, I teach it as the stick being parallel with the drum head. As of late, I've been trying to get them to play taps at 4in, just to get the taps to project a little more.

I've been taught (by more than one source) that taps should be the same motion as full rebound strokes, just to a lower height. But the truth is there's no right or wrong.

everywhere i've marched has used 3 inches for taps. as for whether the stick is paralell to the head or a little above, well that depends on the stick angle in relation to the playing surface. for example, at highschool 3 inches was defined as putting the bead paralell to the head then turning up a little higher, but at corps its defined as paralell. the bead still ends up at basically the same distance from the head though b/c the angle we used in highschool was more shallow than the one that was used at the corps i march. not to put littlesnareboy down, but cadets don't have a defined 4 in, they use 3 for taps, and im almost positive crown does also (lee marched cadets).

In my line tap height was 4 inches but i just thought about it like someone on here said just a note that is not accented if that makes sense. lol

our taps are around parallel but we play six or about ten degrees up for our higher tap