The quantity of onions can't have anything to do with the final flavour, as long as all the other ingredients are balanced pro-rata.
I don't know so much George, from what I have experienced so far bulk cooking can and will have an affect on the finished product. How much of an affect is where I think the question lies. I certainly wouldn't make up a quantity of base similar to a BIR, I wouldn't be able to store it or use it enough to warrant this.
Despite the argy bhaji of base recipes etc, I still think we're pretty close. I ordered a meal for the wife and I from our local decent TA (not IG) which contained Lamb Do Piaza Mushroom Rice, bhaji's, pakora, Prawn Puri and a bread and I have to say that apart from the Naan the rest of the meal was no better than my best efforts using recipes from this site.
So this book is going to have to go some to make impression for me on the BIR front. Does it mention what restaurants were used for the undercover recipes. I'd certainly like to know if they are the modern style BIR or old school restaurants.