Hi Grimmo,
I don't know if it is a generall thing all over the country, but I find that BIR curries these days tend to have much less oil floating on the top than they once did.
The other point I would make is that I have learnt recently that the pre cooking of meat / vegetables is sometimes done in large batches in a seperate "curry sauce" that isn't blended and therefore has seperated oil and a certain amount of different curry sauce which is added to the base sauce in the final preparation of the dish. ?I'm not sure if this going to help us get closer or just put another spanner in the works, but I know that it is correct at some restaurants. ?The seperate curry that the meat is cooked in is sometimes recommended for children although it is not a true curry but it is mild and very tasty.
Hope this helps and not hinders our collective progress,
Cheers,
Blondie