I've been told that for the best sound the beater should strike the drum head in the center of the head
This is true. The only disagreement will be over what "best sound" you are after.
Maximum punch = hit in the middle, maximum tone and complexity = hit off center. That's because hitting off center excites the higher modes of vibration in the head relative to just the 1st vibration mode (which is center going in and out). I used to have the address of a nice little demonstration of this. But the wikipedia entry will do:
http://en.wikipedia.org/wiki/Vibrations_of_a_circular_membrane
Notice that someone worked out that this was perhaps too technical for most readers to understand. Clever. I wouldn't have noticed. Did you?
Anyway...scroll down and there are some animated giffs which show what I'm talking about.
If you try it with the beater hitting a bit above center and this sound doesn't please you (after dealing with matters of head tuning) then the next thing I'd do is try one of those Remo Falam Slam patches (or Evans patch, or similar) where the beater does hit. Or get a quarter (or similar sized piece of metal disk) and stick that on the head using tape (gaffers, duct, whatever you have). Put a couple of pieces of tape right over the coin. See if that helps. What it does (or the falam slam patch) is once again shift how much of the energy is going into which vibrational modes. If the tape/coin test shifts the sound in the direction you like then you might want to invest in a Falam Slam (or similar).
Remo: http://www.remo.com/portal/products/2/599/613/dh_falams_slam.html
Evans:
http://www.evansdrumheads.com/EvAccessoriesPatches.Page?ActiveID=3576
I've used the Remo falam slam patch (on a coated Remo Ambassador) on my 18" bass where the normal height beater hits 2/3 of the way to the top. No problemo, plenty of punch. The falam slam (or quarter) moves the sound profile in the direction of more punch. So if that's what you find lacking with off center you have some cheap experiments to conduct.
