I'm not quite sure what you're getting at regarding lift perpendicular to the leading edge?
If an aircraft is descending at a steady rate, ascending at a steady rate or flat on the tarmac, the force counteracting gravity must be the same - whether it's due to the wings, terra firma, or helium bladders in the fuselage. For our purposes it's likely to come from airflow over the aircraft, so the question isn't how much lift there should be - we know the answer to that - but how it's produced.
Perhaps we're talking about slightly different things - lift defined as force perpendicular to the airflow will change slightly because the angle of descent changes in a slip. In fact, it must increase as we need the vertical components to remain equal.