Bad aim?

[Mikey]

Exactly my point. If you're travelling in the same direction, relative speed is only the difference of the two, and hould lead to less misses than "normal."

[Duskofdead]

True but a lot of battles are chase battles. So although they appear to be not moving much they may be moving very fast.

Logicaly, that should make it easier to hit.
For example, say you're in a car going at 60 MPH. Another car passes to your left going at 62 MPH. If you were to take out a gun, it would be trivialy easy to hit that car.
The same with Trek. Even if one ship is going at .9C, if the other one is going at the same speed, or similar, then it should be trivialy easy to shoot it down.

Even though we've never seen anything remotely similar in canon, one thing I always thought would be "smart" for a faster ship to do (and I used to do this regularly in Star Trek: Generations, the game) would be to "flee", but occasionally get back into weapons range just long enough to fire aft weapons, then slip back out of weapons range again until another volley was ready. An enemy would be stupid to keep pursuing you unless they were faster. I guess the in-universe explanation of why we never see anything like that is because at the extreme limits of weapon ranges, practical targetting and hitting becomes very challenging.

[Mikey]

There is also the question of firing arcs, etc. While it is intuitively a good tactic, I think the fear is that it will actually lessen the total firing time, and therefore total "lead on target," that can be brought to bear.