I don't have an offset firebox smoker but I do have a rudimentary understanding of the physics of heat and smoke.
Yes, adding the smoke outlet modification to mid level or slightly lower will help with the air mixing and smoke flavor. It will also help even out temps.
Without the smoke outlet modification the heat and smoke will rise and ride the path of least resistance along the top of your cook chamber to your outlet. What you end up with at the grate level is radiant heat while the majority of the smoky hot air is flowing above your meat.