Its simple really. Any kind of pipe or hose has an internal resistance to flow.
The longer it is, the higher the resistance.
A shorter path would produce less back pressure unless you throw some bends to compensate, or as some people do throw an adjustable baffle in the exhaust path. Then you can adjust the flow restriction accordingly. (this is usually a washer on the end of a bolt threaded into the headed or midpipe)
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