The fundamental machine is a Wedge not a Ramp.
An upward sloping Ramp can be a Wedge if it is used to provide mechanical advantage in elevating a load. Distance/Effort. (Screw thread)
A downward sloping ramp provides no such advantage, In fact it's a disadvantage. A braking force. So therefore a downward inclined plane is not a wedge and furthermore not a machine. No mechanical advantage. It's just a downward sloping plane.
Not all ramps are equal.