Sorry, there is no vertical in 2d, there is simply length and width, or if you prefer X and Y axis. Vertical is only in 3d or if you prefer the Z axis.
The only time I can see height making a difference is in the Heroic tier where there is limited flight and limited large monsters. I mean, making a Wall of Stone 10' high or 20' high just changes the DC to jump or climb it, unless the difference is going to the roof.
Once flying becomes common, height no longer makes a difference unless it goes to the roof. And once teleportation becomes common, walls are pretty pointless...