That key damper section is the double wall appliance adapter that I had on hand from a previous project. I know I don't need the damper but I don't look forward to replacing that whole section. As it is, the operating shaft of the damper sits in oversized holes that are leaks into my flue. So not only is there junk in the flue but the leaks also hurt draft. Ugh, I suppose I ought to look for a smooth adapter as step #2 after bumping up the stat to 1.5 tonight.I'd get that key damper out of there. You won't ever need it.
I will add that my stove is barley closed at 1.5. At 1, it is closed more firmly.
The manual, as I recall, spec'd out the minimum length for installation in a mobile home which I don't have but the stove doesn't know that.