First of all, it assumes that BB doesn't raise, and that BTN always opens with the same amount (when he opens).

Also, it ignores ESS, implied odds, and, basically, all the poker that's going to happen between PRE and showdown.

It omits any knowledge of Villain's ranges or post-flop tendencies, as the OP was concerned with ranges in the beginning of a HU match.

It was really only meant to be an introduction to using bet/(bet + pot), and to see an application. Also, given how tight OP's ranges are, I was motivated to show him how he's likely throwing away monies by playing so tight HU.