Do you have options for having the sceen higher? 29" is going to cause you problems. The people in the back row will have difficulty seeing over the front row. Trust me, I had to raise my 10ft wide screen higher from my original measurments. My back row is sitting on a 8" riser platform.
Normally, you want the eyes of the people in the front row to be 1/6th to 1/3rd from the bottom. I personally prefer 1/6th or lower. Some people do not like to sit up during the entire movie, and like to recline a bit. If your screen is to low, you won't be comfortable watching the low screen.
http://www.cinegi.com/cgi-bin/riser.cgi
