This system has a 12" round and a 8"x20" split trunk. Duct system is all metal.
The tech is up against some retro-fit type issues because of structure limitations. I was adamant that I would not cheap-out and settle for a basic design. The tech is going through all the motions I see advised here and is consulting up his chain. I do not feel I could ask for any more attention to the design.
He does have a full 1600cfm (normal design w.c.) of return from 5 locations. With the second story being slightly under a positive pressure.
I know much of this useless from a critiquing standpoint over the internet.