A great result, James. I think many do not realise just how SQ improvement can be made with some care speaker adjustments and sympathetic room treatment.
I did a similar exercise a few months ago, and using REW measurements as I made changes I could not only hear the improvements but also see the changes in the frequency response at my listening position. I started tuning the speaker postion to its optimum within my room constraints and then added temporary dampers(curtains, fleece throes) and removed or cover up reflective items(TV, pictures). If I hang old thick curtains at the 1st & 2nd reflection points this really improves imaging and definition. I have put 2 art acoustic panels on the wall I face when listening and this also helps definition. On the wall behind me I put up all my old CD shelving and CDs randomly spaced along with some other objects this also helped. From the REW measurements I could achieve more improvement but that would mean installing bass traps and that would be a step too far for SWMBO. The temporary curtains at the 1st, 2nd reflection points I put up on 1m poles I hang in hooks on walls when I feel like it.