Geez, my last post is a grammatical nightmare. I'm fortunate to have been given an Ipad for some rocket heater work I did for a friend, and I am really enjoying sitting on the stove's bench with it, but it's not helping my posting quality any. Sorry about that.
Anyway, Mike, I think I am probably well north of you, hold on....
Ok, you are 39.62N and I'm 48.11N. My weather is weird though, I have only a handful of days below freezing, and only a handful of days above 70, due to my proximity to a consistently 50 degree F ocean. Single digits are almost unheard of, maybe once every few years we'll get that cold at night. Here, the biggest problem is light, which is why I haven't bothered with a stove in my greenhouse. I'm on the north side of a 2,000'+ hill, so I get very little light from November to March. Not only that, but it's mild enough here that I can go down to the garden right now and pick cabbage, brussel sprouts, a variety of mustards, enough kale to choke a horse, chard, and some other stuff I discover when I poke around.
Back to the stove. What I meant is that in my experience the mass, if built up at least 6" in every direction around the flue pipe, will take quite a bit of consistent burning to dry completely. Until it does, the stove won't be running at it's full potential. So, due to that, I always encourage people to start drying the mass out asap, and add on to it as it becomes dry. Trying to do a huge mass on the first go can often lead to a difficult first few weeks, if not a month, of difficult performance, as the exhaust is way cold compared to what it will be. One thing that helps a TON, in my opinion, is covering the mass to get the temperature up. Put some blankets over it while you burn and I bet you'll see it's average temperature go up by 100 degrees. In that way you can get warmer morning temps if you go to bed when it's 200*F instead of 100*F.
What I meant by adding on was that if you are waking up to the mass being 50* when it started at 110*, if you doubled it's mass and got it to the same temp, it would be much warmer in the morning. So, I'm not saying to change your exhaust layout, but rather build up in height and width around it with cob/rocks. You will reach a point where your average burn is long enough to heat the whole thing, and it has enough mass to maintain the temp in the hoophouse until you return to burn it again. It will be a balancing act, but looking at your photos I bet you could easily double the mass and still be able to warm it in a reasonable time.
Do cover it, old Goodwill blankets or something will go a long way to bringing your overall temperature up. Then you can play with when you cover/uncover to suit your schedule the best. Oddly enough, I find it better to cover when the stove is warming up the mass, uncover while it's running and up to temp, and then cover again for the last part of the burn and leave it covered when it's out. It seems counterintuitive, and I may be wrong (again), but I find it keeps the mass temp up and therefore the space as well.