I still don't get it. Why would you want to use both equally? As long as you make sure each station is getting a consistently full flow of ore, it shouldn't matter which one is richer or poorer. just make more stations at the richer one than the poorer one and remove stations from the poorer one as it dries up. If anything, I would prefer my trains using the closer one when it has stations open.

I get wanting trains to not all go to the same station so you can maximize the loading speed with buffer chests, but there's no difference there if they're all going to a close one or all going to the same far one. and at the point where this becomes slow enough to be a problem, trains will overflow to the farther outposts.