Due to the fact that the focal distances in the guide are somewhat changed I assume you should now put the triplet 320 mm in front of the collector. BUT! Where is that measuring from? The overal center of the triplet? The back of the triplet? The front of the triplet?

Actually the lens must be GREATER THAN the focal length from the LCD. It's not placed in relation to the collector fresnel, it's placed in relation to the LCD. Since the actual distance between LCD and lens will vary based on the distance from the lens to the projection screen, the actual measurement is relatively unimportant. However, the distance is generally measured from teh center of the lens assembly.

If the lens is closer than the focal length, it will never achive focus at any distance. At exactly the focal distance the focus is "infinity" -- It is only when the lens is greater than the focal length that it can ever acheive focus.

My understanding was that it should be measured from the back lens. As stated above, as long as you allow for some travel in your focus mechanism, it should not be a real big deal, but I went from the back lens, and it worked out well.