Thanks for the quick reply!
Firstly, I think in terms of fixed location or shown where you press, the latter would have to somehow define what stick to show depending on where the user touched the screen, which would diminish any real gains the 'on press location' system would have. Probably be easier to make dual stick controls be a fixed position, but allow us to define the position in Mobile Game Settings?
It would be great to name them too, so they can be easily referenced in the blocks of behavior designs, and assigning a different set of images would be helpful, more so on the outer ring which could contain UI elements for example. This isn't essential if the sticks are fixed in a user defined position, because we can create additional UI if required, so just a luxury
The only scenario I can think of, off the top of my head, for having more than one stick would be a local multiplayer game where you could control 4 characters for example (which could be really fun!) - this could be really interesting, actually!