are you sure you were sending them to me......
There should be clearance at the top, the diffuser has been made to accommodate the majority of the exhausts available for the 350z. I guess if there was too much of a gap at the top it wouldn't look right, it would look like the diffuser was floating
You can see a couple of pics of different exhaust with the diffuser here:
viewtopic.php?f=180&t=58971
Thanks for the feedback and a nice guide to fitting