Can location at x,y,z see the sky returns true if there are slabs or stairs above?

I'm using can location at x,y,z (xyz of event/target entity, which is the player here), see the sky, and if player is under slabs or stairs, it returns true, and I don't know why this happens. I could probably check every block above the entity to see if they're slabs and stairs, but I wish this would just work. Is there any easy fix for this?