this is how i always thought passing works:
in the playbook when it has the % for the different levels, very short, short, med... I think the way it works is that those are the percentage of routes in your playbook that would be at those distances.
Some coaches think if they set it at 10-20-50-10-10 as the distances that 10 percent of the plays will be ALL very short, and 20 of the plays will be ALL short, 50 med...
but the way it works is every play has a mix of these distances. the mix depends on the levels that you put.
in the example above, if you ran 100 pass plays out of shotgun that would be 5 wr on routes, multiplied by the 100 plays and what you should expect if you expand f the play by play is that of those 500 routes, there will be multiple routes on each play and they would occur at the rate set.
Then when you set your formations and the target %, it will decide who runs what routes during the plays.
If you set your RB to 100% on all plays, he will be the primary target on all plays, and because 50 is the highest of all of your routes %, he will run the med route as the primary target. other players will run the other routes because they have too. But if you set your RB as the primary med target, you could set your wr as your primary short target, and your wr2 as your deep target, and on play when you run those three routes, those players will run them as you set.
I am not sure if this is all 100% how it works. I run the ball a lot. But this is how I understand it works.