Paul from Lockgate Stoves had a look at the stove today. Excellent service explaining what he was doing and why. There was a small leak around the regulator then running under the stove. Paul removed the regulator, set it back up on his jig in the van, and changed olives and nuts on the connections.
He removed the stove and cleaned up the diesel underneath.
Low flame is massively lower than before, explaining the high consumption before.
The Facebook Reflex group is helpful, but there are nuances with these stoves. I had a look at the instructions for adjusting the High and low flame screws, but they are for a Toby regulator and unlike many Reflex stoves, my 2062MK has a different regulator, and you have to turn the screws the other way.
I was advised to call Lockgate, and it was the right advice. The stove is running well, and I feel like I had a crash course in running and maintaining it going forward.