I'm fascinated by this 'fusion' playing, can anyone dissect it for me?

Grangousier

Also, fiddling some more and avoiding work, I realised that the higher of the two dominants is the flat five sub of the lower - with a bit of voice leading F7 - E7 - A major sounds very 19th century. For example:

x        x        x
4        3        2
5       1        2
3        x        2
0       2         0
x        0        x

F7     E7      A

Voice leading may be putting it a bit strongly, but there it is. No help at all with the widdly, but it's the sort of thing that entertains me.

viz

Grangousier said:

But Phygian dominant is the main one used in fusion after harmonic minor.

Not a very learned person, but one thing I noticed when I tried this out is that if you add a note between the seventh and the root (there are reasons why you might want to do this) - in this case an Eb - you get two dominant seven chords a semitone apart - in this case E7 and F7.  Which also sounds good if you weave them together.

Nice