It can't push you out of your square, but it can force you to move within your square to avoid damage. (i.e. make a reflex save).
It can't "force" you to do anything. If you fail your Reflex save (or don't attempt one), you take damage, but you obviously
didn't get out of the way.
Besides, you can have the Flaming Sphere "jump" up to 30 feet when moving it towards someone. If I jump it so that it comes down from directly above them, are you saying it will "hover" over their heads, rather than landing in their square?
Of course not. It will land on them if they fail their save, and then - since it can't push aside an unwilling creature, and it can't fly - it has to come down somewhere. It can't end up in the middle of the square, so it can only "occupy" the part of the square it ends up in.
If 3E physics say that you can't be "between" squares, then those same physics have to accept that a 6' diameter ball of flame can occupy the same square as a Medium creature,
without burning him except when the conditions of the spell are satisfied.
If you prefer realism in your game, then the rule that should be bent is the one about being between squares.
Isn't "I move three squares forward and one square diagonal"
more CRPGish than the rule under dispute?
How do you account for the fact that a wizard stuck in the same space as a 6 foot ball of flame doesn't need to make Continuous Damage Concentration checks to cast?
How do you account for the fact that a successful Reflex save does not, in fact, move the creature into the next square? How did he avoid damage while remaining in the same 5' space as a 6' sphere?
Since you agree that it can't force you out of your square - only to move within your square to avoid damage with a successful Reflex Save - then obviously, there is
somewhere within your square where you don't take damage. 'cos you end up standing there with a successful save. If you just stay in that part of your square next round, and the Sphere is not moved, shouldn't it still be "safe"?
-Hyp.