... I do plan to use an acsoutically transparent screen and that is one of the last things I need to buy now. Not cheap. I'm not sure at the moment how high the tweeters are but it was all a compromise between seating height and where I thought the screen needed to sit. I have yet to run Audyssey so I should probably reserve my questions for when everything is setup and ready to go. I usually find that I'm standing up near the back of the room while evaluating sound and picture which is probably a bad idea as I would never stand to watch an actual movie in the room.
We're using an acoustically transparent screen by Seymour, and Audyssey MultiEQXT corrects very well for the transmission loss (only a couple of dB at the top of the frequency range, and truly transparent below). That's from the MLP -- I haven't measured it far off axis. The dialog is crisp and clear. Seymour is very good about answering questions, such as how far away you have to sit to not see the fabric pattern. We are about 12.5 feet away from a 130" wide (width, not diagonal) screen, and the fabric pattern is completely invisible.
By all means wait until your room is completely set up, and you have run Audyssey, before evaluating.