I believe that thinking of slap/finger/garrison(or dipiazza or just four finger technique) as separate entities requiring large shifts in position and way of thinking is folly. They are the same, the only difference is a small shift in your right hand and a different sound coming from the instrument.
Nobody thinks playing 2 finger over the bridge pickup is a different beast entirely from playing over the neck pickup, why should slap, double thumb, four finger etc all be seen as such different forms of playing?
Watching a player like Wooten or Manring really shows a fluidity in right hand technique that lends itself towards expression and sound rather than simply "slap bass" or "four finger plucking". The same way a great guitarist doesn't just run through sweep arpeggio patterns and call it music but rather uses the motion as a tool to get through a sequence of notes that he has written.
Anyways, that is my 2 cents and silly rambling...
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