Faster downwash, slower downwash?
If you have two helicopters of the same type, side by side at the same DA, same RRPM, one at min take off mass and the other at max, the speed of the downwash would be the same, just the heavier one has to push more air. Surely the speed of the downwash is dependent on the RRPM and the amount of the downwash is dependent on the disc loading?