Since there are lots of questions on mounting and CIH calculations, I'm posting more instructions on how to use the Mitsubishi HC4000 Online calculator
to decide the mounting options:
1) Decide on the size of the 2.35 screen width
first. For example, I planned a 110.5 x 47 screen so for the calculation purpose the 110.5 width is what you plug into the "Screen Details" width and press enter. It will automatically calculate the corresponding 16x9 height and diagonal which is what will be projected ultimately. For me, this worked out to 110.5 x 62.5 = 127" diagonal 16x9 image. Make a note of the difference between the height of the 2.35 image and the height of the 16x9 image. This would work out to 62.5 - 47 = 15.5 inches.
2) Then, enter the ceiling height. If you have a 100" ceiling, input this figure and press enter. The calculator will give you the distance between the floor and bottom of the 16x9 image. It will also give you the distance between the floor and projector bottom. Your aim should be to maximize the distance between the floor and bottom of the image by changing the pole and image diagonal setting. Forget about the offset figure - practically it isn't very relevant because you have other figures to guide you.
3). If you are doing CIH, remember to add the 15.5 inches to the distance between the bottom of the image and floor. For a 100" ceiling, 5" pole and 110.5" image width, the maximum distance between the floor and image bottom would be 8.4" (as per the calculator) plus the 15.5" (due to shifting up the 2.35 image digitally) resulting in 24" almost.
4) Make sure that your projector throw distance falls between the Longest and Shortest. To my understanding, irrespective of whether you physically move the projector or you change the zoom, the offset will be the same for a particular image size.
5) Verify these figures with the projector central's calculator. Use the 16:9 option only. I'm not sure how accurate the 2.35 calculator would be (I never tried it).
In my opinion, I found that for a throw of 13.6 feet, the image size of 110.5 x 47 was optimal in terms of brightness, clarity, lack of pixel visibility and size. I could increase the height by another 1-2" maximum without changing the brightness significantly but that was the limit. Going beyond that resulted in a significant drop in brightness on Low lamp mode. Anywhere from 45-49 would be ideal I guess. I know that there is a great deal of subjectivity involved here but this can be taken as a starting point. Others who are running a CIH can probably confirm this. Also, as you can see in my previous post, I've painted the screen wall black so the black bars that are projected above the 2.35 screen are completely invisible.
EDIT: While discussing the slight drop in brightness due to the size of the CIH image, one of the forum members suggested that I switch on Brilliant Color, which gave me a boost in lumens without necessitating changing the lamp to high. This is what I recommend to those who are planning a similar setup to mine and who don't want to sacrifice lamp life or change gamma.