Blackbloodtroll's got it right. Turn that 2D grid into a 3D cube and reach should work just fine. A creature's reach extends in all directions, even up.
About a relative topic, my group has a good running argument questioning whether a vertical threat counts as flanking when paired with an attacker on the ground.
This commonly comes up when flying and nonflying pcs or monsters are working together.
I always argue that it is not flanking, unless their is also an attacker threatening directly under (so you can draw the imaginary line straight through the cube).
About a relative topic, my group has a good running argument questioning whether a vertical threat counts as flanking when paired with an attacker on the ground.
I always argue that it is not flanking, unless their is also an attacker threatening directly under (so you can draw the imaginary line straight through).
To flank you would need to be on opposing boarders or corners, when adding flight, swimming, or raised terrain and changing the battle map from 2D to 3D, that should still hold true; a line would need to pass through opposing boarders or corners. Thus, if one person is directly above, then the flanking partner would need to be directly below. If one is above and to the left, the other would need to be be below and to the right, and so on and so forth. An airborne attacker should not count as flanking a foe when paired with an attacker perpendicular to his or her location on the ground, so if I'm understanding you correctly, I believe you are correct.
It does create the odd situation where a 3 foot halfling and a 7 foot half-orc can both reach the same 10 foot shelf without any issue, but neither can reach the 11 foot shelf without a little jump. But you already have that with horizontal reach, so it's not that much further a suspension of disbelief.
That small and medium creatures have the same reach has always caused some suspension of disbelief. I think it's historic and for balance reasons that they do.
Yes it gives strange situations, so as that 7 ft halforc only occupying a 5ft cube, and only threatening 3 ft upwards so to speak.
But I guess it makes more sense than say "medium creatures occupy 2 cubes" though. If you attack someone in the next square you can lunge and take a step forward, etc, but you can't really do that when attacking someone above you. So I guess it's ok if the reach above you is seemingly a bit smaller.
Hope that made sense :)