yes US gallons - sorry I keep it that way since everything else on the plane is US gallons - 12.5 UK.
This is leaned although running higher rpm (24) - at higher alititude/lower rpm it can be leaned down to 12 gph ( 9.9 UK). It does lean off much better at not significantly higher altitudes, but UK flying is often very restrictive, especially with class A ceiling around here.
I do agree that from what I have seen of the Diesel engines they screw the short field performance. I see the CAA/GASIL are warning people to be more careful when shortfield working on diesel engines.