Stephen,
well pleased you're doing well on the curries which is obvious from you're posts (i always aim to read).
have you a link to the recipe you're using.
i had used the longish green chilli in the past with the squat green being used as garnish only ie thin slices across the chilli. by fine chopping the squat chilli and adding after the base it's taste seems to spread across the sauce. i don't see it being added for heat which at the moment i'm getting just from the chilli powder. vindaloo would be different (lip burn).
the sultana gives a taste i can't describe. i 1st used it "cooked" in adovada and felt it resembled the taste of the restaurant madras. a sanity search pulled up chewytikka's chutney (
https://curry-recipes.co.uk/curry/index.php/topic,6116.0.html). this is the basis of my thoughts. no vinegar though.
paprika in the mix powder is a further factor as the BIR version has a hint of "bluish" in the restaurant due to the lights which give it away. i know it sounds mad but the inclusion of paprika seems to fit the bill.
i'm still a good way off matching the taste - hence the post to gather any pointers that have not yet dawned on me.
next up is to try out the common (say asda sultana) and the Asian store offerings of golden and green.
best wishes