Pipe size is dictated by the engine parameters in header design and not the number of bends typically. The rshared_pm and valve events will largely play into overall length of tubes. Valve size, engine size, and port size are the main parameters that determine the tubing ID and steps. When you send off to burns for them to design a header they provide a properly sized collector for you and tell you the length, diameter, steps and step locations for the header as designed around your engine using their analysis. Their designs arent always the absoltute best but they are real close. You just have to do the math correct to figure the linear pipe length for each bend depending on the degrees of the bend which is simple math.

What you are describing is kinda like the equivalent straight length method of sizing tube/duct based on pressure loss of the elbows which is useful for fluid systems but pretty much discarded in header design. Less bends the better though.