It has nothing to do with the cursor position, but for snapping to a surface to work, you must ‘see’ the surface you want to snap to! So your viewpoint is important, not whether it’s in Perspective or Orthographic view. In order to be able to snap to a floor, you’d have to be in Top View, when using Orthographic.
Placing the 3D Cursor on the floor probably only works because the floor is flat and on the 3D ‘floor’ (Z = 0). When the surface you want to snap to is uneven and/or ‘floating’ in the 3D Space, that wouldn’t be so easy (you’d have to snap the Cursor to the floor and then you might as well immediately snap the chair to the floor…)
