You should also consider doing the same on the walls(or add a bevel) to give the wall/floor separation/depth. You can see some examples using BOTH effects here and here.

BTW, I also used the dodge/burn tool to give those even more depth. dodge helps darken up the darks and makes for a deep "looking" drop off. While lightening up the "top" of an elevation chance a bit gives just a bit of contrast that really sells the offset between light/dark, high/low.

Oh... and good job there, you have the idea well in hand... I would probably go a darker closer in to the "ledge"(pretty much pure black and with perhaps a slightly larger fade area), especially with the large elevation change you are trying to depict.