Am I reading this correctly? Are instructors teaching that it is not allowable to join downwind? CASA's pretty picture shows the downwind joining position as being by mid field and the crosswind technique as being mid field at the completion of the turn onto downwind, that is to say, you turn somewhere near the upwind threshold so that you are established on downwind by half way down the runway. The radio call comes at the mid field position and that is where other traffic should then expect to see you.