Thanks for being objective :)
Glad you remembered to take off the support rings.
Yea, the inward cup is to miss the Makerbot's frame. Wanted a deeper grill than the flat fan fare that you typically find on Thingiverse.
All the same, most shrouds have a negative impact on air flow, surprised it's close to 8%.
Perhaps you would be kind enough to test some of my other designs:https://www.thingiverse.com/thing:1795614https://www.thingiverse.com/thing:1750976