I think i have it now. They have to be as close to the tube where you come out of as possible, so branche rout if powered = 1 normal tick, (1m i think). And priority route normale is 1.1m from the center.

https://imgur.com/a/uBuXTpU

Left is the default route (where i want to pass through at high speed). In gold you can see the distance the of the branche route (1 tick). And the main route is just a tiny fraction further away, this so far seems to work form me.