PS: drop shadow only displayed on one side

I am making a Drop Shadow for a layer but I want it to only show up on have of the object. When I set the angle and direction, no matter how small I make the shadow, if the distance is small enough for part of the shadow to be under the closest side, the shadow also appears on the top and bottom of the object. I would like it if I could just earse the parts of the shadow that I dont want but that just changes the shadow to fit to the new shape… Does anyone know how to earse part of a shadow or make it small enough to only be see under one site of the object in the layer? Thanks