There is no rule positioning the inbounds players other than they cannot break the out of bounds plane. They are free to move anywhere within the inbounds playing court right up to the plane. The out of bounds player has the responsibility to move back to create space, that is why they ask for 3' back depth. The dashed line WAS the out of bounds line until the ball was touched inbounds, completing the inbounds throw attempt, thus a player within the dashed line, or bouncing the ball in the dashed line is officially out of bounds.