Hey Loisk, this might not help much, but then.....
Get yourself sat comfortably on your F3S & settle yourself & your RH mirror where you can see behind you (remembering that ideally, you should see very little of you or the Spyder in the mirror, & more of what is behind/alongside you) Then set your LH mirror as close to being able to see behind you on the other side in that mirror when you are in the same comfortable sitting position just by turning your eyes/head, basically you shouldn't hafta move your head much at all!! Then once you've established your position, move closer & up or whatever until you can see what you would like to out of that mirror & tell us here which way you had to move & how far, ie forwards 6" & rising up 3" or back & down whatever.... Like I said, might not help much, but then again, it might just trigger the response/info you need!! Or maybe it'll reveal how you could move the mirror to compensate - I dunno, but I reckon it's worth a try!
BTW, I don't think moving the mirror arm forwards or back out of its central 'locked' position is a good answer; on one of the demo Spyders I rode, I tried doing that cos I could only see the ground immediately behind the Spyder (Lois is a little shorter than me) so I adjusted the mirror up & out as much as it'd go & then pushed the arm away from me until I could see behind the Spyder - but as soon as I hit 80kph/50mph-ish on the freeway the mirror arm slipped back into its useless locked position.... And that was on a dead smooth freeway too, no wind or traffic buffeting worth mentioning, & no pot-holes or bumps etc.... so it was just wind from the speed of travel! It seems the LH mirrors here are pre-loaded the wrong way for our Aussie cambered roads, without mucking around with them, they give us views that don't help much!! Maybe I shoulda tried swapping the mirrors to the other side of the Spyder?!?