That #vi half diminished seventh chord that you analyzed in Mozart's Symphony no. 40, I would probably just analyze as iiø7/V because it's clearly going to V, it's not in some like chromatic diminished chord passage where I feel #viø7 would be justified.
Good point. In my experience, however, it is not very common to use any other chord as the top part of a secondary chord besides a dominant or leading tone type harmony. An exception to this would be a ii - V - I progression where both the ii and V are acting as secondary chords to the temporary tonic.
That #vi half diminished seventh chord that you analyzed in Mozart's Symphony no. 40, I would probably just analyze as iiø7/V because it's clearly going to V, it's not in some like chromatic diminished chord passage where I feel #viø7 would be justified.
Good point. In my experience, however, it is not very common to use any other chord as the top part of a secondary chord besides a dominant or leading tone type harmony. An exception to this would be a ii - V - I progression where both the ii and V are acting as secondary chords to the temporary tonic.