left and right are only from your perspective
from the perspective of the character he is either above the platform or below it
but that said you can call it whatever words you like, left, right, up, down, it does not matter, it only matters under which condition which angle should the character have
you could even pin invisible sprites above and below the platform and make one blue and another red and say when the character is overlapping blue then X and if he is overlapping red then Y