The inheirant problem, if i remember correctly as it was explained to me, is that at night, the max visual distance of the AI, is 60% of what it is during the day.(edit: and i think this is hardcoded, like alot of other things in this game
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which means if a unit has a 9,000 KM max distance, it means it can see 5400 KM at night. After that point, weather and enviormental variables come into play, and your looking at distance of around 3,000 KM, give or take 1K.
The only solution that ive been able to find, is to reduce the max distance. ( Ie, 60% of a smaller distance = you get closer to ship) Unfortunatly, this effects daytime performance, so theres only so much you can do.
The solution is probably in creating larger waves or increasing the wave factor (in addition to adding extra visual nodes by unit type) . However, larger waves are a problem in SH4, because thigns like to blow up, sink, or submarines stop recharging their batteries because they think their submerged. Increasing the size of the waves, i think might be the anser, but its a HUGE kettle of fish, IF.. IF.. its the answer.