Tiny creature pushing opponent

[Forseti]

I'm not sure if there's a rules answer for what I'm about to ask. I couldn't find one, but that could just mean I missed it. This is something about to come up in a game I'm playing in, and even if there is no readily available RAW answer, I'd like some opinions or references to similar situations.

So here goes: my Magus has a tiny familiar, and I'm planning to have it deliver Force Punch spells. Obviously, it'll have to enter the target's space for that. With a successful touch attack and a failed saving throw the spell will push the opponent away from the familiar in a straight line.

How do we determine the direction of this straight line? Does it have to be in the same direction as the movement that took the familiar inside the opponent's space? Or, is there a case to be made that the familiar, taking up only 2.5' x 2.5' of space, can position itself within the opponent's space in such a way that it can push in whatever direction it chooses? Finally, could it push a flying opponent downward?

[Byakko]

When you're in a square, you're generally considered to be anywhere and everywhere within that square. While it could be argued that no specific direction is "away" from two creatures in the same space, it should probably be ruled that you can push them away in any direction you want. In any case, the direction the familiar entered the square from isn't relevant.

Handling odd 3D movement situations isn't covered thoroughly in the rules. This is one of those things a GM should adjudicate on a case by case basis, imho. If the familiar can fly or otherwise conceivably position itself above the creature, I would let it try to push the target downwards.