I am still wanting to experiment with ludicrous 3" primary headers to see how they act on a supercharged engine. If that were to capable of being made workable, then 6" primaries would be next LOL.
"Correct backpressure" is "Deep space vacuum"
I know that in a pulsed-flow system, you take advantage of the elasticity of the air to "pull" exhaust out of the port using the rarefaction of the air to do so, even as you utilize the elasticity of the air to create a springy cushion of air just waiting to burst forth into the combustion chamber when the intake valve opens.
I know that the best way to achieve appropriate frequency match between peak rarefaction/compression is VELOCITY, just like throwing a softball attached to a slinky as hard as you can will result in more stretch than weakly tossing it.
BUT, at some point, the tradeoff between the power needed to create said velocity in a finite-sized pipe/conduit and the pumping losses at higher RPM/flow volume becomes greater than the advantage in power production.
The cam profile could be designed to optimize response to the stupidly-large exhaust pipes, but alas, the very thing that would take advantage of the sizing at high RPM would be, no surprise, detrimental to low-RPM operation.
Ideally, the intake and exhaust tracts would resize on the fly to produce maximum power and minimum restriction. This is possible with existing technology, but the cost would be higher than a static tract design.
I know it's about finding the right balance, but for every single RPM, load, throttle opening, etc. there is one absolutely peak, ideal, perfect set of parameters of lift, duration, tract size, header configuration, etc. Varying each of these on the fly to perfectly match each possible situation would be a work that only God himself could do, but that does not change the fact that for every given desired level of power output, there is one ideal set of parameters for it.
Having said that, I think there are more precisely-sized and shaped designs for headers that are out there, yet undiscovered, because discovering them costs money, and producing them may cost more than has been the norm.