Most Toto 12" toilets will actually fit an 11" rough-in. It does seem a bit strange that while we expect exact measures in almost everything, toilet rough-in measurements are not precise, but that's the way it is. I have 2 Toto toilets, both flanges are set at exactly 12", but the toilets have over 2" space behind the tank. I think you will be fine with the Drake II. My suggestion is, get the toilet and set it on the flange without a wax ring so if it is too tight, you won't have to clean off the wax.