Shooting from South to North also has a minor range increase.
You can also gain more range by firing your front and rear guns during ideal range times.
E.g. if you turn your ship away from the enemy (after sailing parallel), your rear guns will stick out slightly and allow you to gain a few mm of range.
The same will work for your front guns by turning towards the enemy, but obviously be quick to turn away after you fire if you don't want to rush.
Use Z and C to isolate your fore and rear guns respectively. X activates all guns again.