I hate to really even touch this question because there are alot of unknown variables but if he is moving to his left that is prolly the angle he is comfortable attacking at. Does he swarm from that angle? Is he orthadox? Counter puncher? Now of course your right is gonna be there but but dont sell it of course. The classic and most simple counter to someone who is moving to thier left is to take your right foot and take one step to the outside and throw the straight right and they will run right into it. But of course its not always that simple.