Random question.. intake exhaust crossover with headers ?

Headers have a specific job to do, which is to deliver a low-pressure signal to the back of the exhaust valve, at the exact right time so that just before it closes, and as the intake is simultaneously opening, this low pressure signal is transmitted across the top of the piston and into the intake plenum, where it yanks the A/F charge, that is "just waiting" in there, towards the chamber, giving it a head-start, on the intake stroke.
Now, if that crossover passage has NOT been blocked off, think what will happen?
Yes that low pressure signal will travel right thru the passage to the other header, thus destroying at least two signals, and knocking out 25% of the power that the overlap period would have brought to the table.
On a stock-cam 318 engine that's probably no big deal, cuz it only makes about 16* of overlap. But as the cam gets bigger, by the time you get to a 268/276/110; this cam is making 52* of overlap, which as far as overlap is concerned, is a lot.
With the crossover OPEN, IMO, the two pipes involved will just shuttle hot exhaust back and forth all the time, same as the logs do when the flapper valve is open.