I too have had issues with Mages tinkering with max placement to get as many bad guys and no good ones. One of the best solutions I saw recently was to let the spellcaster pick the square and then roll randomly for which of the four corners the spell centered on. This has the advantage of being quick in play and generally letting the Mage pick his spot, but with the small variation they have to take some care casting into close quarters.
It will be interesting to see if the revised rules deal differently with spell centering, so that it is no longer on an intersection.
