I have been testing freighter stuff.First of all upgrading your freighter engines and trader modules have no effect on the freighter once it gets in the loop.The speed will go back to one and there is no jump in trade value with more trade modules.Second,it says near your home planet the trade route value gets less,but that seems to be only outward bound,after it returns it holds the highest value until it reaches it's planet of origin.One way they might make trade more effective is the faster engines you have,the higher value the route by a small percentage.Meeting customer demand and all that.A second way is to have a tech where the gravity well of the destination planet slows the freighter or stops it for a few turns while in the highest paying part of the route,thus increasing its value.The same could apply to its return trip.In a large map this is a way you could protect your trade route by making fewer routes more lucrative and getting more value for the ones you have tucked away in a safe zone away from the wars going on.