Size one missiles are generally used for anti-missile work, as such they need to be as fast as possible, at that tech level perhaps 30-40,000km/s ? If being used for antimissiles you don't need much range, I doubt you'll have a resolution one sensor/fire control with 500,000,000km range, and even if you do, that's the range for a 50 ton object, you'll get less range against a small missile.
So I suggest making a new engine for that size 1 missile .6 size, maximum speed multiplier. halve your fuel, then see what range you get. Then design a resolution 1 sensor and fire control as long range as you can reasonably fit into your Ships or as big as you can afford to research.
About resolution, missiles don't care what size target you fire them at, as long as you have picked it up on active sensor with any ship in range, and as long as the ship firing the missile has a fire control also within range of the target.
Sensors are best tailored to the size of the target, you can't just make a massive capital ship sensor and expect it to be good at detecting destroyers or god forbid fighters/FACs.
So for instance, a heavy long range missile carrier might have a resolution 150-200 sensor for detecting very large ships at extreme range, your destroyers might use resolution 80-100 for detecting destroyers, and smaller beam armed escorts might have resolution 20-40 sensors for detecting Fast attack craft. Then just put a fire control onto your missile ships which matches the resolution of whatever sensor you're using, and with enough range for your missiles, you should aim for making every missile as long ranged as you can, at least limited by the range of your sensors. But if you have alot of sensor ships picketing a system or your fleet you could just make extreme range missiles and cross your fingers that teh target stays in range of something.
