image size and prjection lens

Ok, here are my questions.

I am planning my pj and so far i have a 15" LCD and MH lamp, ballast. I have done all the calculations to figure out what lens i need and the throw i want etc, BUT....... I am looking for a projected image of 80" - 100", hopefully no bigger than 100 because i want to save the quality and brightness, plus i think 100" is enough. I want to put my projector behind me at about 14' ish. I did a calculation and put 96" for expected image size, 15" LCD, throw of 14 ft. Came out to be 576.65 mm FL which is a long and hard to find a lens with a FL around that length and probably expensive.

So i than thought of having the pj at about 6 ft from the screen (in front of me when im on my couch) and i forget exactly all the values i used but the FL ended up being about 320mm which is perfect to use the 80 mm projection lens that is being sold on a few sites. BUTT... i then though that pj has to be somewhat higher up so theres not to much of an angle facing up higher on the screen. Which would make the pj in the way of veiwing the screen and make it annoying. Ive read that you can fix this by having a split fresnel setup ( am i correct) but the unsplit setup has a better quality projection (am i correct?) so i dont know what to do? I would rather have the pj behind me so i could have it lower so there little or no angle but i dont want to spend over $100 on a lens. I am from Canada too so everything will cost me alot more ...... Anyone have any suggestions?