Hi emin-j, interesting post again. The amount of oil that ends up in a final dish through base /paste/cooking/marinade etc becomes, IMO an ingredient in itself. The oil supplied & used for mass production / trade will unlikely be the same product for retail as is the 20kg curry powders. A bit like paint for example. The likelyhood of home cooks using trade oil I would imagine would be virtually zero.
It's probably a missing ingredient in recreating the bir taste at home but not entirely essential i have found.
of note: Some people i know in Glasgow have a small restaurant serving Scottish produce, small menu, very little spice. Before opening, the aroma from their kitchen is similar to a bir, without the spice. a bit of garlic aside & the smell is oil
@curryhell~ I think the base provides far more flavour than I previuously thought. Many dishes here are sweet(ish), not korma sweet. Im sure it come from the base. An owner told me fairly recently he uses coconut in his base & 3 other bases he uses(i think he meant pastes) Stick the usual madras ingredients on top of a sweetish base & the results are outstanding
Regards
ELW