The thing is that the ship can break off after launch, which, if far enough out, should allow it to avoid action.
True, but in that "railgun vs railgun" example, wouldn't the reasoning go like this :
1- railgun to-hit probability are a function of range (the square of it, if we're in 3D, this, btw, is a real problem with a 2D aurora...)
2- therefore, the best launch site is when the flyby ship has the shortest trajectory to target
3- this would be known to the target, who can now send (in advance) a hail of projectiles on the ship final approach
4- in this setting, evasive maneuvers
after launch become useless, the incoming ship could avoid this either by launching earlier, but then, longer ranges means lower to hit pb, or by 'wiggling' while it flies by
I find this last point interesting : somehow, we are assuming that, in NA, fuel is spent to accelerate, but in fact, in "combat mode" (ie wherever you might be target) perhaps we should consider ships spend fuel at all time to make minor trajectory changes, in order to avoid enemy guns... And the closer the enemy might be, the more precise its guns, the more you need to wiggle while you fly.
Francois