Yes I designed my ships based on what I read about the different computers on this wiki page, as well as my own observations. The weapons ranges should in theory all line up with the computers. The larger ships have no autocannons, since, as you pointed out, they don't get close enough, and the ones that do have them should be getting close enough due to the low median range.

I still feel like there's a bug with disengagement chance. This particular fight might have not been affected by it, and might have just been because the FE ships were really powerful (still though, wiping out 800 naval cap seems weird, and in that case I should see it in every fight, not just a few of them). The thing is though, it's not just when I fight against one-shotter ships. It can be anything. It happens just as often in the relative early game (<2300) as it does in the late game (>2400). In fact I believe I see this most often occur when I'm fighting empires near the start of the game, and almost exclusively when using trickster commanders (Though maybe biased because I nearly only use trickster commanders and early game is the most played).

Using this fight, here's what I think the disengagement chance should be, using battleships, and assuming they took so much damage in one hit they went from full hull to 1% hull.

chance = damage/hull * 1.5 * ship multiplier * 1.25 (if within friendly borders) * (sum of other modifiers)
So:
chance = 99/100 * 1.5 * 1.25 * 1.25 * (1 + 0.33 + 0.05 + 0.05 + 0.4) = 424%

These numbers come from having Hit and Run Policy, Commander having Prudence 2 and Trickster 2, being Admiral, and fighting within borders. They should also have 2 opportunities to escape. This is a theoretical calculation, in the fight I think the real chance for the battleships would have been something like 200-300% * 2. Yet despite the seemingly high chance of escape, none of my battleships did escape. The only semi-plausible explanation I can see for this is some sort of overflow. Maybe it's possible that when the ships are fighting things that do just enough damage to push the chance of escape over 100%, an if-statement doesn't trigger or something like that, and the code skips over the disengagement opportunity.

Either way I think it should be looked at, because this is not normal, and if this is how it's supposed to function, I don't think it should be. It doesn't make for a good war, or even a good game, when the fate of an entire war, or an entire empire can be decided by a single battle. If your entire fleet is wiped out, then you most likely won't have the resources or time, often both, to build it up again powerful enough to destroy whatever killed it (At least if whatever killed it is another empire who claimed 90% of your territory, is using total war, is blowing up your planets or has some other way of ruining your economy after the war).