On the lower pictured header I assume someone used an undersized pipe and the edge there of is your concern? Meaning the overlap is in the wrong direction? I'd think in an all out race engine buzzing at high RPMs with only a header it might be an issue. But, once you put a muffler on a street car it likely becomes a greater restriction point than the issue presented. You probably only want a 2"-2-1/4" max anyway.