As far as my experience goes (about 660 hours) there is no saying - you have to just test it manually by looking at your trade income with different merchant configurations. Theoretically there is a bonus to your trade power if you have all your merchants steering to your homenode, but in my games it was always better to use all the merchants to collect in the nodes where i had power. only if you completely dominate your homenode (like venice) should you steer there. in that case it could be better to use all the merchants to steer to your homenode, because they also add some value to the amount of gold they send to your homenode. Hope that helps, if anyone nows more about this or can correct me: please do!
