All movement in the game is orthogonal (up, down, left, or right). Diagonal movement is never allowed, so if that's what you were trying, then it wouldn't work. If you were trying to pull the mage towards you up or sideways (meaning the other mage went from 2 spaces away to 1 space away), then that would work fine. Force push can move the target in any orthogonal direction regardless of the direction from the casting mage.