In Christopher Schlegel's 'A' Section Chord Changes, he presents the 1, 6 (#1dim7), 2, 5 forms, and then the alternate higher forms.

In the higher forms, he actually shows the A7 as an alternate for the C#dim7, which sounds great. My question comes when he explains that the C#dim7 is actually a substitution (the 7 of 2) for the original Am7 (6 chord). In effect, how does the higher A7 work to 'replace' the originally intended Am7? Their major and minor aspects seem to conflict (not in sound, but certainly on paper).

Mind you, everything sounds good, and I'm hardly questioning his judgement here—just trying to learn why/how this works.

Thanks!

ch: