Here's a rule of thumb: The engineers design their projectors generally that if you are sitting directly underneath it, and the zoom is right in the middle, that is a very nice picture. So for the Z4, the projector 10 feet back placed in the middle of the throw with the seating 10 feet back the general rule would be a 74 inch diagonal. Therefore to answer the OP's question is yes 92 @ 9 is too big.
Keep in mind there is room to fudge. You can scoot in and out a little bit, also a textured screen can hide screen door. However I tend to lean more towards quality over quantity.