Steve, I agree with Matt. Left to right is most important since that's the longest length and will be most noticable (because the further away you go, the greater the level change will be so the level difference will be most significant on a long run.) When you look at the side, it's only what, 18" or 24" wide? Just get that close as you can without disturbing the left-to-right level and you should be good.
Also, whenever you HAVE to be off somewhere... I'd recommend having it tilt towards your overflow(s) instead of away from them if you can.
Also, whenever you HAVE to be off somewhere... I'd recommend having it tilt towards your overflow(s) instead of away from them if you can.