[Slick]

All weapons degrade hit probability at 10% per square until a minimum of 1% is reached up to their max range.

From settings.txt:
Combat Base To Hit := 100
Combat To Hit Modifier Per Square := 10



So you start at 100% at range 0, which is really 90% at range 1 because ships can't occupy the same square. For every square beyond that, you lose 10% chance to hit. 2-3 squares means 20-30% which is probably what you are seeing.