After some amount of pain with sushi belts, I’ve just stolen the design from Nilaus with passthrough filtering splitters and bots, so very much similar to your setup but two main belts.

https://youtu.be/qr_Lep5UCJU?t=37m2s

Not at pc so don’t have a BP but basically like this:

You do have to account for the omportant secondary outputs of the recycled overflow, so green circs, iron and copper plates, iron ore etc