If you descend with the Heavy and Light helo at the same speed, pitching up both the same manner you get exactly the same initial downwash speed on both helos (refered to the helicopters)
The only difference is the deceleration rate, at early stages the heavy helo simply falls through the VR, with the higher integral downwash compared to the light to the environment.
Also the deceleration rate plays a role. Wich is for shame not linear, now try to get an nonlinear speedchange in an windtunnel.
Disc load itself is only a mathematical simplification for power calculations since the blades on varying modern day helicopters are nearly equal.
A smaller disc is actually providing a VR, since the outer vortex has to be smaller, the proper reasons for higher disc loads are:
Smaller diameter provides landing nearer to obstacles
Materials, for shure(since we have seen that tapered blades also provide VR)
Blade systems (with more blades the diameter decreases)
Greetings,