Instead of scaleable, constant mini-bonus I'd rather see a small modification to the damage roll table. First, let's make the game marginally easier by deciding that on an attack roll, if it's very very good (beating the difficulty step by a lot), you have, say, 2% chance of doubler damage (on top of the normal random). Then, we add a rule that as you go up in Accuracy, this 2% goes up, probably to around 20%. So every time you hit the enemy dead-centre (which will happen a lot with high-Accuracy people firing at short ranges), there's an additional roll to check if the target's life is even worse.
Alternatively we could limit this effect to Aimed shots, but make it more likely to happen.
Stat bonuses aside, this would place sniper rifles buck where they belong: experienced snipers, not rookies who need Accuracy training. (Though they still can do so.)
