Following situation:

1) A-Wing parks right on top of a small asteroid marker. But one side of the base overlaps the boarder of the asteroid marker by about 5mm.

2) TIE SF would end its movement on top of the A-Wing. If the A-Wing would not be there it would be considerd a collision since it would land on top of the asteroid marker.

3) Instead this is not considered a collison with an asteroid since I would bumb into A-Wing base.

4) TIE SF is moved along its manouver template until in contact with the A-Wing. TIE SF base is not in contact with Asteroid marker but onlt with the A-Wing base whitch parks on an asteroid marker but sticks out by about 5mm.

5) TIE SF looses its Action and is prohibited to attack the A-Wing. But it does not have to roll for damage and may attack another target except of the A-Wing since this is not a collison with an obstacle.

Right? Or is this a collision with an obstacle too.

The TIE SF would only suffer the effects of the obstacle if its end-position places it over-top the obstacle in this case.

Ok, so in this case it would only suffer the effects of bumbing into the a-wings base?

Yup, so no action & can't shoot the a-wing

Per the Rules Reference, Page 14:

"If a ship overlaps another ship, only the portion of the maneuver template that is between the starting and final positions of the ship is counted
for the purpose of overlapping obstacles. Ignore the portion of the maneuver template that the ship moved backward along to resolve the overlap."

So if the Awing prevents the Tie SF from landing at the end of the template, then the TIE SF would not be considered overlapping the obstacle and be free to attack other ships in Arc(s). No damage or effect from the obstacle would come into play.

Thank you all for clarifying.