As different films/movies have different aspect ratios on a front projector you get a different size of white borders above and below the screen depending on the aspect ratio of the program.
I find it a bit distracting and it reminds me of how bad relatively my black level is versus CRT or other display technologies....
I am currently using a DIY fixed frame screen and in order to mask out the white areas , I just had my wife make a black cloth w/ garther that I could adjust to mask out the white areas depending on the program being shown...whether 16 x 9 or 1:2.35 etc... I have one on top and another at the bottom
The idea is to place a black border on the picture and it really makes a big difference in the contrast ratio percieved... For pull down screens maybe a velcro runner on the wall behind the screen will do the trick so that you can run black cloth across the screen..
For me it was a big improvement to the overall projected image....
