nope, not reversed..
if I go to a dyno with 2 rollers or with one roller I can already see up to 20-30hp difference at speeds above 200kph. if I do not measure this losses, so only know the whp I cannot compare..
If I do measure this losses and add them to the measured power at the rolls, I know bhp (or at least the power to the wheel with taken in account the losses from the tyres on the rolls) so then normally when all is done well I should be able to run tyres or rolls with different friction properties and still come to approx the same calculated bhp
I agree with your premise of different WHP numbers measured based on different number of rollers, etc., but I respectfully do not on the part of where you take these differences to arrive to a calculation that arrive to the more-or-less the same result at the crank. If Dyno A and B give different WHP results, it is more accurate to try to correlate those variances to a corrected, maybe composite value
while still at the wheel, rather than to take both results and back-calculate using factors and arriving at a figure at the crank. The reason is that error and uncertainty ALWAYS and inevitably stack-up as you go through more transformations. In your approach, you would be taking wheel power, which is already - as we perfectly agree - notoriously subject to variance, and stacking up the uncertainties posed by tire deformation, driveline friction, slip, etc., to get to a crank HP figure.
At the end of the day, the power that is transmitted from the tire treads to the street pavement are what gets you from point A to B in a given time, so correct WHP is much more consistently and precisely correlable to real performance than whatever the engine is putting out and being divided/dissipated through the drivetrain. Talking (accurate) WHP also puts a decisive stop to the testosterone-induced but mindless talk about "my engine makes moar powaah than urz" because the buck stops when the light turns green and we don't have to debate about 300 HP TDIs that can't even break into the 13's on the 1/4 mile - much less in the low- to mid-12's where it should be capable, assuming 3000# - despite all the excuses, "I had no traction mang.. I wuz spinnin the wheels AND slipping the clutch on every gear from start to finish!"
Physics can be such a b!tch sometimes.
This further reinforces why I believe there is some merit of getting more than one set of results from different dynos, knowing how notoriously susceptible they are variations between different installations.