I own a vw1000es, but the principles are the same. Please refer to the following manual.
Your calculation of 45.5 inches is taken from page 91, which refers to an installation using a PSS-H10 projector mount. Are you actually planning on using this mount? I'm not sure you can use an extension pipe with it. If in fact you can't, you shouldn't use this mount.
If you're not using that mount, here's the way to calculate what you need to do. First take a look at the pictures on pages 16, 22, and 23 to get a general idea of whats going on. Then, look on page 17. Under the column marked 100, on the 4th row (marked y) you will see that the center of the lens can be at most 34 7/8 inches from the center of the screen. This is assuming the projector is horizontally DEAD CENTER with the screen (x is equal to 0).
The center of the screen will be 9 foot - 57 inches = 51 inches from the ceiling. So the center of the lens of the projector must be at least 51 - 34 7/8 = 16 1/8 from the ceiling. On page 93 of the manual, you will see the bottom of the projector is 3 3/4 from the center of the lens. So the bottom of the projector must be at least 16 1/8 - 3 3/4 = 12 3/8 inches from the ceiling. Assuming your projector mount is at least 3 3/8 inches tall, then a 9 inch pipe would technically be ok.
However, I don't recommend you cut it this close. You won't be able to shift the picture left or right, which means the projector will need to be horizontally dead center with the screen. In practice this is hard to achieve. Furthermore, you will be using the edge of the lens, which typically is not quite as sharp as the center.