Thanks for the suggestions.
I've dabbled with extra hot chili sauces but, to my mind, they are similar to commercial curry pastes in that they also add a particular (unwanted) additional flavour (i.e. preservatives, acidity regulators, etc) which I have never detected in a BIR phal.
I've also added various fresh chilies (including habeneros) and find they also add a flavour which I have never detected in a BIR phal.
I've also played with dried chili flakes and dried chilies (similar, I suppose, to your suggestion about crumbling fried, dried, chilies Gary), but I've never seen parts of chilies in a BIR phal either.
My best guess is that they pre-fry extra hot chili powder to get the rawness (and perhaps some of the powderiness) out of it.....I think I need to play a bit more....

Any other suggestions (preferably based on actual BIR observations) would be most welcome
