I have to be honest here, You would gain so much more efficiency and heat by installing a stove on the first floor with a couple old style grates in the upstairs floor (it worked for 200 years and our ancestors were very smart) LOL.
If the stove MUST be in the basement you might do better to gain some radiant value by insulating, cutting a vent/grate in the floor directly above the stove, etc. I know everyone loves the literature on this model, but i assure you that its impossible to have a wood stove design function efficiently with coal (people can say what they want and spec sheets can be printed with efficiency ratings and BTU outputs and this argument could go on forever but i will keep saying the same thing... wood and coal require different grates, different shapes, different design, different airflow and to think both can be done equally well in one stove is a myth).
Ive never had the opportunity to test this unit but it must burn through coal like crazy looking at the depth of coal bed vs surface area? does this burn through the night no problem? do you have to bank up coal against the rear into an uneven bed in order to get a long enough burn? why is this design not made anymore?
Please understand I hope im way off base and hope someone with more smarts then me can think of some magic to get this working better for you, but it appears you have gone through alot of good efforts here to make this work and im just giving the suggestion that it might be better at some point for you to try a new tach. wishing you the best new year ever and some more warmth too