After much time I have most of Slic3r clear to me but I cannot work out how to apply a filament config to an extruder. For example if you have Dual_L.ini and Dual_R.ini then whichever you have active in Slic3r filament tab will become "filament" in Slic3r.ini. It seems that in the platter view the top one is assigned to Right and the lower one to Left but it is really confusing and sometimes it seems to pick one at random from the filament directory.

I have it sorted so that I can do separate support prints properly but I wanted to be able to set separate configs up for left and right and left-support-right-model and right-support-left-model.

Does anyone have their head round this particular bit?