The accepted convention I have always been taught is that one AR is on the near post A12, his job is to make sure it goes inside his post and also over the crossbar.
The other AR is further back around G2-G4, he is checking it goes inside his post (left hand side one).
Generally the near post AR will see it go inside his post and over the bar and shout "yes", then wait for the other AR to shout Yes, or No.
If however it goes way wide, to the left as we look at the diagram, he might shout "your call", i.e. it went left of my post, but might have gone left of yours as well, you decide?
If it goes right of the first post or under the bar the first AR will shout "no" and thats really game over.
Two Yes's, flags up.
One or more No's, flags stay down.