Volker, just my 2 cents regarding previous comments:
wing mirrors - my understanding is that most wing mirrors were dealer installed, not factory. I have a BN6 and the mirrors are just over the front wheels, so I guess there is no designated "correct place". The concern I see is that the bottom seal on the side curtain overlaps the base of the mirror.
soft top shape - In order for the side curtains to close properly against the soft top, you would expect the shape of the opening in the soft top to generally match the shape of the side curtain frame. In your photos, the top of the soft top openings angle downward front to back, rather than the ~horizontal top of the side curtain. Likewise, the rear of your top openings angle front of vertical compared to the rearward angle on the side curtain. It's been a long time since I put a new top on my car (maybe 1984??), but I remember having a lot of trouble. In my case I finally discovered that the ends of my top frame were rusted and deteriorated (the part that sticks into the hole) and were actually ~1" shorter than they had been originally. This caused the frame to sit too low in the car and could explain some of the mismatch if your car suffered the same fate. However, even after fixing this, my fit was still far from perfect. I chalked it up to the 2-seater's top design being a bit "hinky" to start with.
Rich