As to the topic of this thread I should say that I'm making curries with a BIR taste most of the time, but it's not quite 100%, and that's why I asked if anyone else has got the consistency down. The missing pieces for me probably just come down to things like ingredient brands, spice ratios, and strength of the curry base etc.
My view is that the fundamental BIR taste is a combination of onions, GG paste, spices, and reclaimed oil. How accurately this taste can be reproduced at home will vary from person to person because of their own preferences and the techniques/ingredients used by their local curry houses, but I definitely think those four elements make up the majority of the "secret".