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Shorties, as the picture is referred to, do not have any "scavenging effect".
And that is what headers are all about. Each tube on a header helps the other cylinder tubes "pull" exhaust from the cylinder quickly and efficiently. The longer the tube, the more scavenging.
Then the cylinder can refill again with a fresh mixture = more power.
However,
Shorties, are basically all show / no go, manifolds.