It depends what you want to see from afar. For objects/ entities it's in the general "video settings" options, in the game's menu, and we don't have very precise control (no numbers). For structures, it's in the gameoptions.yaml : DSLDistancePlanet: 3000 << distance in meters at which structure becomes invisible DSLDistanceSpace: 4000 << same, in space
You're welcome ! In fact I would have answered right away if I had seen it, but I was not around when you posted it, I just saw it late yesterday and thought " damn ! such an easy answer, and that guy has been waiting 2 days ?!". You'll see, you can crank this number at least to double, and POIs will be easy to spot and not pop out of the blue just when you're in range to get shot.
You can change the "when the POI is loaded" setting (DSL, as Kassonnade explained) but the visibility distances (how far you can see a POI or Entity) are fixed and cannot be changed.
Follow-up questions. Which gameoptions.yaml should we edit? The one in the save game directory or the one in the scenario we play? Does one take precedence over the other?
The gameoptions.yaml in the scenario folders is always just a template that gets used as the defaults when creating a new game using that scenario. For games that are already created you always want to edit the one in the save itself. Edit the one in the scenario folder to change it for new games you may make in the future, that way you don't have to edit with every new game created. Has no effect on already created games. Keep in mind if it's a workshop scenario or a scenario that comes with the game then the gameoptions.yaml in the scenario folder will be reset with game updates or workshop updates, as well as when verifying files through Steam.