One thing I should have mentioned is that it was under 40° for the entire cook. On my Green Egg, outdoor temp. has very little effect on cooking. With my new offset, I'm sure I burnt a lot more logs than I would in the summer.
This would decrease your efficiency even further and facilitate more fire/air moving through your smoker. Compare the fuel you used on this oct recent cook with doing a brisket on your Egg.
I'm not familiar with the tuning plate but what I have tried to remember is a traditional offset cooks from the top down, rendering the fat, why the top rack doesn't give the best results. I personally wouldn't be making any modifications to my smoker after just one cook with so many variables. Hope this helps