After some additional testing for the A/A1 and A/A2 sights I cannot find any discrepancies with the reticle respectively with the simulated collimator functionality.
I come to the conclusion it is a self-inflicted ergonomic issue. Being to lazy to adjust head position in VR (be it by seat height or head position) I lived with a disadvantageous reticle position (upper border of projection glass) which subsequently led to unnecessary head movements when trying to follow the reticle leaving the projection glass which again led to upper body and therefore right hand movements (=bad for precise maneuvering).
Conclusion:
The not exactly small dispersion of F-5 guns + ignoring basic ergonomics = bad combination.
Rifter's post in Gun reticle accuracy and seat height [user problem] was marked as the answer