After counting numbers from the inserters, I've came up with these proportions:
Iron: 3 lanes, 0.4 : 0.4 : 0.2
Copper: 3 lanes, 0.33 : 0.33 : 0.33(evenly distributed)
That's how the belts are divided by the splitters in this build.
The inserter stack bonus is +2. You would probably get twice less production without bonus.
10 min production graph
Blueprint string
P.S. Thank you so much, Daniel!