Been thinking more about the mechanics of avoiding patrol ships, such as after a pirate raid. If your drive plume can be spotted from most anywhere, that's going to be tough. How long can you burn before someone's sensors can determine your direction? Not very long I'm guessing. So either a very long trip on the float, or your burn hard for a while, then use auxiliary thrusters to modify your course so the pursuing ships don't know your exact heading (then still along trip on the float). So any known destination, the patrols will likely be waiting for you. We can always have a system that just abstracts whether you get away undetected, but the narrative needs to make some sense. This part needs some work to be playable.
I would say there are basically three levels of detection you need to have an estimate for:
1) Energy Output which results in you being "spotted"
This means "if the opponent is not aware you are there". If you've launched from a carrier which jumped in out-system and have been silent running on passive sensors the whole way (one nice thing with main drives being obvious is that passive sensors are good enough to plot intercepts with). Closing to intercept, your target gets regular checks to see if you're spotted, and the higher or lower your thrust the greater the check difficulty varies off the basic roll. I would say you'd make this check either once an hour or
each time you change range band relative to the target.
Note that if overhauling from astern, you'll have to be doing at least the thrust of the ship you're chasing; even if you're only closing at an effective 0.5 G, you're putting out a 1.5 G drive plume behind you.
Frankly, I'd suggest anything above a 1G burn is going to be spotted within a few rounds by basically everyone close enough to give a damn about it. You might be able to hide your drive plume from someone you're overhauling because the ship itself blocks a lot of the radiated energy, but that's (a) an imperfect solution as it'll spread out fairly fast and (b) assumes no-one else who does see you tells them about you.
2) Energy Output which results in you being "tracked"
Pretty much exactly as before, but when the target is actively looking for you. If you go 'dark', but they know where you did that, then the threshold for them spotting you again when they're using more sensitive 'tracking' instead of 'search' sensors is going to be much lower, as the sensors are lavishing greater sensor exposure time and processing power on each 'frame' in the relatively narrow field of view near where you dropped out of sight instead of sweeping a continuous 360' x 360' pattern.
This is going to be a lot tougher. Basically, you're making a check every round you fire the drives. 'Cold' thrusters are possible - something like vapourising LHyd is going to have far less of a heat trail - and if you want to put out any meaningful acceleration whilst 'dark' is probably a required choice.
3) Energy Output which results in an "accurate plot"
Just because you can go "there's a ship there" doesn't mean you've got an accurate value for its acceleration and heading. This will be a bit more forgiving than being 'tracked' - so if you do a fast burn for a few minutes to get out of range, they're still following. You go 'dark' but coast - they can follow (at range) because they know your heading when you cut your drive.
If you fire thrusters, they may or may not pick it up, but the odds are that over, say, half an hour of continuous burns, they will probably spot one or two burns. That means they know you're still there and roughly which way you're going. Only if they spot, say, three on the trot, do they have an accurate bearing on you again, at which point they can fire at you and you need to lose them again from scratch.
This would require X 'track' failures within Y rounds - with the difficulty reduced according to the duration of the burn and the range.
As to figuring out where you're heading; if you are heading towards an obvious world, then yes. They can accelerate continuously and you can't - there's no way to get there first. But I would assume you would never accelerate directly towards your ultimate destination if fleeing under stealth....