I had a severe look into vignetteparams.ini and I can see where the missions are generated but I could not find any reference to distance.
There are references to preliminary battle and main battle - these are when your target is not there, so you hold off his cronies; then you get a second waypoint to the main mattle when you either finish off all his cronies or they run away.
You could change the decision nodes to ensure you get a preliminary battle always, or other stuff too, like ensure you always get a solar.
I tried searching but can't even find my own post to point you at it, the search engine doesn't look in titles it seems.
Why do you guys want to change so much of this game anyway?
Roleplay: - the art of self-deceipt!