Nonlinear speed changes in wind tunnel. Tricky. That's why they researched VRS on sleds
Embarassing that I didīnt thought of it.
See Sokol, that's why you should read Prouty ... and some NACA papers ... or Castles and Gray who did wind tunnel research on VRS. I don't really see a problem with wind tunnels. It is better than real live, because you can keep the helicopter in that area with the highest turbulence for any length of time, while flying in there on purpose and staying there is according to researchers rather difficult. Prouty thought, that the pilots got only a highly transit state during the test flights.
At the same downwash speed, the heavier ship will fall faster into or through VRS. Is it that what you mean? In that case, that would be obvious. Otherwise I still don't get your thing with the constant downwash speed either.
By the way, the formula would not be that much different. There is a similar formula that uses the rotor diameter. Blade load or disc load is more or less the same thing. It only gets ugly, when you want to find out the regions where the blade stalls at what Vd and it gets even worse if you have to take blade twist into account.
Who knows, if
this brings us any further.
Known that video for a long time. Been in IT for a long time. Had to deal with smart-arses in IT for a long time. It's not a communication problem, believe me.