If you place the projector any further back than 14.6ft, you can't achieve the screen size your wanting. If you go to the calculator and adjust the bottom numbers to show your desired screen size for 16:9, then look over to the left above that, it will show you the min/max throw distance you can place the projector to achieve that screen size. 14.6ft is the furthest back with no zoom, if you increased the zoom the picture would not fit on your screen.
If your set on that screen size, you might want to move the projector a little closer if possible, just so you have a little more comfort zone, in case you do have to play with the zoom ever.
Hope this makes sense.
On my Z2 at about a 13ft throw distance my 16:9 image is 51" x 90", and that is with the zoom not really being used much.
I would say if you can keep it closer to 14ft or a little less, that would be better.
