I ordered a long cover for our VAH b/c it was in stock and wasn't going to take as much time as a custom-length one. I did what chris_harper2 mentions- the duct and cover stick up in the attic about 9". I forget how I marked it before cutting the ceiling. I'd think it'd be pretty easy to make a template out of cardboard or plywood that'd be rigid enough for your purposes. Besides, a little caulk covers slight misses. Our flue cover, IIRC, has corner reinforcement tack welded at the ends. Cutting would've meant getting rid of the reinforcement and having a less-rigid cover. Also, if you're only talking about 3/4", you could take the hood loose and drop it just enough to mark the ceiling. To me, those options are simpler than finding someone to cut it and not mess it up. FWIW, plasma leaves clean edges, but I'm not sure whether it'd scorch. If you do slide the cover above the attic, I'd make a cover to go over the opening. Then foam or otherwise seal it in place so you aren't venting your kitchen into the attic except through the duct. I made one out of plywood and cut it in two so that I could put it over the top of the duct cover (and around the duct) after the whole thing was installed. Here is a link that might be useful:

Thanks everyone for all the helpful information - questions and answers - on these forums. As someone pointed out, it is hard to know exactly what to do in each case, even after extensive reading on GW. If anyone has the patience, maybe they could help me. I am about to order a Blue Star 48", 4 burner/grill and griddle range. The plan for our new kitchen in our renovated house shows 48" for a hood. Would I be ok with a 48" hood with a 900cfm blower? We don't want an external blower and we don't want to use up cabinet space for a 54" hood unless we have to. Our most smoke-producing activity would be grilling meat. Thanks for any advice.

I believe the big difference is you can get the Bluestar hood in the Bluestar colors. The Prestige branded one is only available in SS. I love my Prestige hood--I splurged on the wall switches too. I was afraid I wouldn't be easily able to reach the hood-mounted switches (I'm 5' 2") but turns out I could. The real issue is it's actually hot up there with the front 22K burner running full blast. It's only like $100 more, and maybe more from the contractor to do it.

It is worth pointing out, I think, that the pressure differential across the blower, called pressure loss, is essentially the same whether the blower is in the hood, at the end of the duct outside, or in a door blowing into an otherwise sealed house. The pressure loss is the sum of all the losses due to friction and turbulence in the duct, duct cap where present, hood transitions, baffles, make-up air system restrictions, etc. Any slight differences in pressure loss with blower position will be due to local transitions where the blower is mounted versus the blower's air flow uniformity at the blower exit. The resulting flow rate will be that which applies to that pressure loss on the fan curve plot. Front of hood deposited grease is due to insufficient overlap and/or insufficient air velocity at the hood aperture. Hoods are generally poor at drawing air from the vicinity of the burners. Most plume capture depends on the plume's upward velocity, mainly driven by the buoyancy of hot grease and water vapor and air. The plume naturally expands as it rises, hence hood aperture overlap is desirable.