I understood the original post, but many of the times you will hit things from a bad angle, especially when you've encircled the enemy, your ships often tend to move around, or phase skim if they have the ability, so the result will be quite unpredictable, and just prolong battles...
I don't know why you assume that a flanking ship's shots will be that much less accurate than those of a non-flanking ship. If you're talking about AI, fine, the AI would need to be adjusted to make it try to be more accurate - and THAT would undermine the point of the mechanic and perhaps counter it entirely. But if you're just talking about general play-of-combat, a ship that's moving around the battle to attack a target from the side or rear is just as likely to hit or miss as a ship approaching from its forward arc.
As far as the "predictability" of shots fired while moving goes, that already exists in the vanilla game - projectiles generally inherit the velocity of the ship firing them, so if you're moving sideways and fire forwards, the shot will track sideways a bit, sure. That already makes flanking harder, in the sense of hit or miss, but A) the AI already accounts for this just like it accounts for leading a moving target, and B) the player can account for this by learning how to adjust their aim based on their movement. Now, I'm a terrible shot anyway, but in a vacuum, would this mechanic make that effect so much worse?