Duncan Fat boy exhaust

[rhandw69]

Im looking at changing exhaust systems. I always try to find pipes that everyone else isnt using but still gives great results. Im wondering who uses or has used the new Duncan Racing Fat Boy exhaust. What i noticed from lookin at in on the internet is that the header pipes seem smaller in diameter than stock. I called Duncan today and they confirmed that as well. My question is this, wouldnt that hinder the top end performance somewhat? I thought that the larger headpipes combined with it collecting up further back towards the silencer, was for a better top end application. Which is what im looking for. I heard the LRD and hetrick head pipes are the same way as well. Not sure if this is true or not, but if someone can explain, id greatly appreciate it.
Thanks