Hi ELW,
The forum does go quiet from time to time then usually picks up again.
I've been trying to do BIR curries for 2.5 years now, usually 2 per week and in that time I've tried about 8 base recipes, 5 or 6 spice mixes and countless recipes.
I'm pretty happy with my results as are the other people I give my efforts to. I can cook nicer curries than a couple of BIRs around here and feel I'm still at the 90% mark.
One thing is missing for me that my fav TA beats me on: A sweet tangy morish flavour to the oil in the curry and I don't mean suggary sweet. It is more spicy sweet if that makes any sense.
I'm beginning to think it may come from the use of whole spices in the base but I don't know which spices and what quantities. That idea came from making the ABC balti base which uses whole spices in a spice ball but for me the spices and mixes were wrong. It did have potential though and the whole spices made their way into the oil in the finished curries.
I could be completely wrong however.

Any other ideas for the sweet tangy taste I'm looking for?
Cheers,
Paul