51.17Level 5 — upper structure over A7♭9

Try B♭ diminished-ish material:

B♭-C♯-E-G.

Those notes form:

B♭°7

and over A bass they yield:

♭9, 3, 5, ♭7.

So:

A + B♭°7 = A7♭9.

This recycles our diminished-dominant relationship.