Just out of curiosity Paul, I understand your air wash reading and your closed primary air, but what was the 'secondary air' control that seemed to be beneath the stove, that your video said was also set at 50%? Have you partially blocked your secondary air intake or does your stove offer the ability to control secondary air flow in some way? Never heard of that before...
That aside, I agree with what others have said; it looks like, in keeping your air wash control half open, you are sending quite a bit of heat up the flue. If you close it down a tad more, you might get stronger secondary burn and therefore keep the temp inside the stove a bit more, whilst also increasing your burn times a little (how long a burn do you get on a full load before you need to reload, by the way?)
My only caveat to that is that there seems to be a third air control on your stove which might change the usual 'rules'.... I'd love to hear some more about that third air control.
Your hearth looks great.. I am always smiling at the way we folk here love to sit in front of our stoves whilst watching videos of other people's stoves! Are there therapies for this addiction, I wonder..?