Oh look, ambushes, another topic done to death.
I will reiterate from all the other threads
"Ambushes" don't work because combat in star-sector is relatively symmetric, because it makes no sense, and because they're already in the game. In a general fleet formation everything is in the same area before a normal combat is joined. Combat ships move out ahead of the main fleet in order to join combat. So if you were to "ambush" an enemy it would just result in all their ships being in the combat... like a retreat action. As a result of this, ambushes are already in the game, when you engage an enemy fleet and its too small to want to engage you it retreats and you have access to all their squishies and combat ships at the same time. In a deployment where you have an advantage of being able to pre-flank with your frigates. You engage in an ambush by maneuvering on the strategic map in such a way as to catch an enemy fleet that wants to retreat.
The reason that this does not work is because of the "fleets are too big to retreat" logic. And the reason that we have "fleets are too big to retreat" logic is because of deployment point logic. Which is necessary because computers aren't infinite. Anyway the deployment logic goes like this "there needs to be a limit to battle size because computers die". And then from there we go "if there is a limit to the amount of ships you can deploy then there needs to be a limit to the size of fleets that can retreat. If there is not then a retreating fleets will overtop the deployment limit and gain an advantage on an attacking fleet. This will be annoying to the player when an enemy wants to retreat and abusable by the player when the enemy wants to attack them"
That is. Imagine a situation in which two 600 deployment point fleets meet each other when the game has a 300 DP limit to prevent computers from dying. If one of them says "yea i will retreat" and the other says "sure i will fight" then the retreating fleet will deploy 600 DP and the engaging fleet will deploy 150 DP. Even if half of each fleet is logistics ships the retreating fleet has a 2 to 1 deployment advantage by retreating. So if the player decides to fight they have 150 DP and if they decide to retreat they have 600 DP. If they player decides to fight they have 150 and the enemy has 150.
Similar things could happen if you, in a big fleet, caught a smaller fleet. It wants to retreat and so does. But because of this it deploys its entire compliment. Thus making the fight HARDER than choosing to fight a larger enemy fleet that would have decided to engage and so suffer from deployment limits. You have 600, they have 400. They retreat and field 200(400) DP of combat ships you field 150... If they had 600 DP instead they would choose to engage. And so your choices being equal (i want to fight this enemy) the 400 DP fleet is harder to fight than the 600 DP Fleet.
Thus we have our dilemma. Players don't think ambushes are in the game even when, functionally they are, they're just defeated by deployment limits logic. Because if they were not then the game breaks. Methods to get around this tend to run afoul of the same problems. They create an abusable system which makes little to no sense.
There is kind of a solution but i don't think a lot of people like it. Specifically its to not count logistics (or civilian ships[even if militarized]) with regards to the "fleet deployment retreat limiting logic". So a fleet of 10 combat ships and 10 logistics ships behaves the same in terms of retreat logic as a fleet of 10 combat ships and 0 logistics ships. This has the side benefit of making it make sense to arm your logistics ships. Because now you actually will have a slight advantage in a retreat action. It also extends the range of fleets for which you can effectively ambush and fixes some deployment logic with regard to be big civilian fleets (which will decide to retreat rather than to deploy a bunch of civilian ships then retreat as soon as one dies)
However it still does run afoul of deployment limitations and so could cause problems for slower computers.(though not as much because civilian ships, due to their lower combat ability should have less of an impact on performance)
edit: Other option would be to remove the "too big to retreat" logic but when you choose to retreat and are otherwise "too big to retreat" you must emergency mothball ships until you're under the deployment limit. This would preserve the fairness issue in retreat deployments. This could cause escaping fleets to dump cargo/fuel afterwards and keep the ships mothballed while a player could do that or just take the massive CR hit from dropping a bunch of ships to 0% CR