In final assembly, I screwed every hole in the tweeter array.
I've talked with the "sound master" and made the same observation on down tilting the cabinets a bit. During sound checks the tweeters seemed dialed in about the 4th row (out of 10 rows). Overall, the coverage was amazingly consistent. The room is almost completely asymmetric, with a glass back wall. I told him to play with tilt a bit, then screw through the brackets into the cabinets to tie things together. We're still learning how to dial in the DriveRack equalizers, so I think we'll get it right in 2-3 performances. It's already light years better than what they had.
Other than the hernias for the guys who put those 50 lb monsters up there, I think the OmniTop12 was the right choice for this venue. The down tilted, melded arrays did a better job than I expected. The only dead spot was the far left rear corner -- most of that got filled by the band monitors.