just an uneducated response with my
Flow sheets show different flow percentages at every level of flow, not to mention that taking the highest lift flow numbers isn't a good bench mark as most motors don't have enough lift to get there any way.
Efficiency of the motor must effect the percentage ratio needed? A highly efficient intake system with lots of inertia must have different requirements than a basic bracket motor, or worse yet a stock type motor.
Efficiency of the header design must play a big part.
In the end, every combo will be unique to itself, having its own sweet spot.
look at the number of cams that are tested on high end engine builds like Prostock or other professional or comp category's and that will give you a clue as to how well a rule like that works. Any one want to buy a used roller cam for a big block? I have three for sale,,,,,,,,,,,,