Help me musically understand "Goodbye Yellow Brick Road"

[Bassaga]

A fascinating bunch of chords and melody throughout, but I'm especially trying to make sense of the part that comes (among other places) at the end of the chorus, e.g.:

I've finally decided my future lies ~~~~~~~~~
beyond the Yellow Brick Roooooad ~~~~~~~~
~~~~~~~~~~~~~~~~Aaaaaaaaaaahhhhhhh

The way it works with Elton holding out 'road' while the 'aahs' kick in is just magical. And unusual. Best I can figure (if you'll forgive my hack terminology) the chorus is in Bb and wrapping up in the same chord, with him singing the last line on the 5 (an F). He holds that note, but the 'aahs' come in over a key change into Ab, on a Bb minor chord, the minor of that original Bb but the minor 2nd chord of the new key.

What makes this transition hit the way it does? Vocals holding the 5 while the chord switches from major to minor? Or the descending key change that hasn't really even manifested itself yet? Or maybe the climbing instrumentals accenting Bb, C, Db to bring out the minor 3 while Elton's on the 5 while the chord is on the minor 2 of the scale that was the flat 7 just a second earlier? Something else entirely?

 

[Mark White]

This is not a channel I've watched before, but this video may give you some insight that helps:

 

[Bob_Ross]

The way it works with Elton holding out 'road' while the 'aahs' kick in is just magical. And unusual. ...[snip]...
What makes this transition hit the way it does?

I wonder if what your ear is attracted to isn't the harmonic vocabulary per se but rather the rhythmic elision: "Beyond the yellow brick" is (arguably) a measure of 2/4 in an otherwise 4/4 piece of music, and so while your ear expects the phrase to continue, "road" is the downbeat of a new measure, which corresponds with the entrance of those "aahs".