Scale Theory: Using Simple Frequency Ratios to Build a Brain-friendly Scale

Only a couple of big gaps remain in our quest to use simle frequency ratios to build a brain-friendly scale: one between Middle C and E, and another between Concert A and C above Middle C. The simplest frequency ratio available to fit between C and E is 9:8, which yields the note D.
You can use the same 9:8 frequency ratio to stick a tone between Concert A and C above Middle C. Call it B.
When you insert these two notes (D and B), you notice a few things:

The scale has no more big gaps between notes;
The smallest gap between notes has a ratio of frequencies of 16:15—not exactly simple;
The order of the letter-names of the notes makes some sense, though not plain, common horse sense. The alphabet starts at C, stops at G, then starts again at A.