I live in Corstorphine in Edinburgh. I don't have a great BIR anywhere near but most are acceptable. Last night, I tried the only one I hadn't tried before on recommendation from my Pakistani friend from work. It was alright, second best in the town IMO.
The thing is, I think I can actually reproduce the difference curries accurately from each BIR. It's quite obvious for the major things what has and has not went in the base. Again, it's quite obvious what has and hasn't went in at the curry stage. Last night's curry's base was mostly onions with some tinned tomatoes, and a shed load of blended garlic and ginger. Not too much tomato paste in the final curry and only a light spicing of cumin and coriander, garnished with some fresh coriander leaves.
What I'm trying to get at, is that after all the experiements, and recipes tried, I think I can actually pick out what's in an "acceptable" takeaways recipe. I'm sad to say, that the ingredients in my favourite BIRs still elude me.