Well, just playing around with your missile tech a bit led me to this design:
Missile Size: 4 MSP (0.2 HS) Warhead: 6 Armour: 0 Manoeuvre Rating: 18
Speed: 32000 km/s Engine Endurance: 55 minutes Range: 105.3m km
Thermal Sensor Strength: 0.055 Detect Sig Strength 1000: 55,000 km
Cost Per Missile: 3.8449
Chance to Hit: 1k km/s 576% 3k km/s 180% 5k km/s 115.2% 10k km/s 57.6%
Materials Required: 1.5x Tritanium 0.0333x Boronide 0.055x Uridium 2.2566x Gallicite Fuel x875
This is keeping with the longer ranges you seem to favor, and ups the performance of your preivous design considerably( it is also size 4, but in general smaller missile tend to be shorter ranged, since you have more limited space for everything you need)
Generally speaking, if you want sensors on your missiles so as to avoid overkill, passives are the way to go, since they require much smaller reactors than active sensors. As well, a tip for missile design that works fore me is to design a junk 0.1 max power engine so I can figure out the exact size of engine I need for the design, and then design that. Keep in mind that the larger the missile engine, the more fuel efficient it is.
A good step by step process of missile design is first, decide what size missile you want. Then, decide what strength warhead you need(making sure it is not below strength 4-which allows second layer damage-unless you need to make it fit or it's an AMM, which are always strength 1). Then, you need to decide what range it'll have, keeping in mind using the 0.1 engine deosn't give accurate range, since it is VERY fuel inefficient; you'll get a general idea of range after a while. For now, a good thing to remember is 0.5 in fuel tends to be long range with a proper engine. Then, put in 0.5 in agility to begin with, and start adding engines. You can add and take away from engines and agility until you're happy with speed and hit chances. Once you've got your engine size, design it and plug it into your design, then go back and adjust between agility and fuel for your final range and maneuver. As an example:
I decide to design a size 4 missile. I have strength 6 warheads, but I decide to just have strength 5 to save on space while still hurting. Therefore, i discover I need to put in .84 to warhead.
I decide on a medium range missile(for me, around 60-75m)
My current engine tech lets me use EPx5 missile engines, so I design(or use an existing) a ep 5x 0.1 size missile engine
using the starting fuel as a baseline, I add 0.5 to agility, then plug in as many engines as I think I need, playing with agility and engine amount until I got both at a point i like
At this point, it'll look something like this:
Missile Size: 4 MSP (0.2 HS) Warhead: 5 Armour: 0 Manoeuvre Rating: 22
Speed: 40000 km/s Engine Endurance: 4 minutes Range: 8.4m km
Cost Per Missile: 4.2356
Chance to Hit: 1k km/s 880% 3k km/s 286% 5k km/s 176% 10k km/s 88%
Materials Required: 1.25x Tritanium 2.9856x Gallicite Fuel x950
I see how many engines I'm using, and what size engine that equate to, design it, then plug in that engine(as an example, the missile is using 20 size 0.1 engines, so that means it is needing a size 2 engine)
I then go back to fuel and see if I'm over or under my expected range. In this example, I'm dead on my range with 0.4 fuel, so I add agility until the total missile size is 4, then I'm done!
Final missile looks something like this:
Missile Size: 4 MSP (0.2 HS) Warhead: 5 Armour: 0 Manoeuvre Rating: 22
Speed: 40000 km/s Engine Endurance: 29 minutes Range: 68.9m km
Cost Per Missile: 4.2228
Chance to Hit: 1k km/s 880% 3k km/s 286% 5k km/s 176% 10k km/s 88%
Materials Required: 1.25x Tritanium 2.9728x Gallicite Fuel x1000
As a general note, this is for a basic no sensor missile. Adding sensors complicates things(but only slightly) as you need to not only make room for the sensor, but for the reactor to power it. This does tend to detract from overall performance somewhat, but on the plus side, when you kill something, all missiles with any type of combat sensor immediately re-target any enemy ship within sensor range rather than simply blowing up.
....You know, I think I'm going to cross-post this into the academy so others can get an idea on how missile design works now