using a damper will result in more coals. area around the damper is a turbulation zone which results in more heat coming off that area of the pipe so placing it near the stove will extract more heat from the pipe. damper is good for draft control in case of overfiring
Considering that an EPA stove has a 2ndary air intake that is always open, I cant understand how "airtight" applies & when the flame dies, the open air passage makes for a nice vent to pull room air up the chimni if no OAK but with OAK , it'll still pull outdoor air thru the hot stove when the coals dont need it & cool down the stove
Install the damper, its fun to play with