After living for a year with my wall mounted Stewart screen (1:1.78, 10 feet wide), I installed automatic drapes using a black velour fabric. This allows easy side masking when moving between the 1:1.78 format and 1:1.33. The elimination of the gray sidebars made a dramatic improvement in the apparent contrast of the picture.
This week I decided to try masking the horizontal bars associated with source material in a format wider than 1:1.78. Using some leftover black velour, I sewed 10 foot wide strips about 16 inches wide. The top masking is fastened to the wall above the Stewart frame, and supported at the bottom with a narrow strip of wood trim. Adjustment is achieved by rolling up the strip on the trim until the width is right to obscure the gray bar. Velcro on the edge of the frame and near the ends of the trim secure the position. When not in use, the material can be rolled up all the way and parked on top of the frame.
The bottom masking is similar, except the top edge is supported by the wood strip, and the lower edge is allowed to hang free. Again, Velcro secures the position.
It takes a minute to put this masking into play, and isn't nearly as much fun as remotely adjusting the drapes, but the improvement in the picture is impressive. The original drapes and the Makita rod cost around $1000 (I did all the labor), but the horizontal masking was only $10).