Look at it as you draw it on the tiller, if it tilts a lot or rocks from side to side then it maybe needs adjusting.
This assumes your tiller rig doesn't clamp the bow or support it on a big flat surface, I'm a fan of a curved support which allows the bow to move, I think it tells you more about the ballance of the limbs.
I don't think a quater of an inch is here or there in the grand scheme of things.
Del