If I understand correctly what you're trying to do, my attached model is one way to do this. In the updated model, the Photo Eye sends a message to the first Control Point when OnBlock is triggered, which then sets a label called "block". Based on this label, further items of itemtype 3 are routed to Conveyor19. The problem with what you were trying to do is that items sent to the exit transfer can't leave the conveyor until they reach the transfer.
