What does Missile Agility do for accuracy that bigger engines doesn't?
I feel like there is an optimal 'ratio of agility to missile size that gives much better accuracy returns than just increasing the speed of a missile, but if you go over it you are wasting space.
Missile accuracy (% chance to hit) is based on the product of speed and "maneuver rating". Speed is obvious; Maneuver rating is (10 + Agility / MSP) and is subject to integer rounding. This means that a mathematical optimum split between engine and agility MSP exists for a given missile design, although it is not easy to determine.
In practice, this calculation has to be balanced against the ability of your missile to beat enemy PD, which is related to speed only, so the "correct" optimization is rarely clear.
What does Missile Agility do for accuracy that bigger engines doesn't?
I feel like there is an optimal 'ratio of agility to missile size that gives much better accuracy returns than just increasing the speed of a missile, but if you go over it you are wasting space.
Basically this especially at later tech levels, missiles have a maneuver rating (MR) that boots to hit chance and agility is how you change it. Don't have the numbers on me but with MaxTech agility I think you can make missiles with single digit speeds that can swat all but the fastest missiles with +100% accuracy.
Thankfully this is not correct... however, at current MaxTech you can design an AMM which has 100% chance to hit any target
and can mount ECCM, and is thus a "perfect" missile. But that "perfect" missile will still be moving pretty fast, definitely not single-digit speed.