Econoburn 2 dampers?

I have been running my Econoburn 200 for a few years now and have always had too much draft with about .04 water column. What I need is about -.04.
I have one barometric damper installed and it is fully open during the burn. It looks like I may have to add another. Does anyone else require 2 dampers in their system to tame down the draft? Is there a rule of thumb for how close together you can put them?
Thanks.

Thanks for the quick response Fred. Dale at Econoburn is helping me work through it so rather than try too many things at once, I will exit this thread for now. I think it may be a matter of my inexperience more than anything.