Hitech, if u look at the real thing installed in a 190, u will notice two interesting points:
1 - The tubes are vertically angled up.
2 - The tubes are horizontally slightly angled towards the nose of the plane.
These points are well modeled in your 3D 109 and 190.
Why the first and second points if the rockets are going to follow the flight path of the plane instead the launcher tube path?
The INITIAL speed of the rocket was 1260 km/h (not maximum speed) and vectored up by the angled tube. IMO, no matter the speed of the plane (for low and medium speeds), the angle of the tube will be mandatory in the rocket proyectile.
I've read something about a maximum speed to fire these rockets, but dont remember that data. Probably, above that speed the effect u described with the dart may be slightly present.
About firing these rockets from a stationary launcher, well, these same rockets were mainly used this way by the ground forces at ranges farther than 7 km. Do you find an initial muzzle vel of 1260 Km/h enough to stabilize?