I can't reproduce the taste or the smell, but then I seem to be looking for something that others aren't.
I think I can put my finger on what is ruining modern BIR curries though or, in other words, what is taking them away from my notion of the ideal taste and smell:
1. Not using a spiced oil, whether specially prepared, or recovered from the base and/or curries
2. Using commercial pastes, notably Pataks'
3. Possibly the use of too much spice. I've settled on minimal spicing of 1 to 2 tsp, not including methi or chilli. Just watch the online BIRs like maliks, they're really ladling those spices in.
4. And last, but for me not least, the lack of use of methi in the savoury curries. Although I think this is more prevalent here than it is in the BIRs (so I suppose that is a complaint about the curries on this site and not the BIR curries!)