Phil, so I just checked both Syed's Basic Curry and Madras recipes and I see a few differences.
1. The Madras has the addition of 1 tsp paprika (slightly heaped?) (at 2:10 on the video), not in the Basic Curry
2. The Basic Curry uses 3-4 TBSP oil whereas the Madras calls for 2 TBSP
3. Kasuri methi is added to the Madras after the chicken, but before on the Basic Curry. Doubt that's an issue.
4. Fresh green chillies added to the Basic Curry, not in the Madras
5. Basic Curry uses 'just under' 1/4 cup chopped onion. A cup is 4 TBSP, so let's say that's 3 TBSP. The Madras used 2 TBSP
Although the ingredient list at the start of the video says 1 tsp mix powder, Syed seems to add 1/4 tsp mix powder (2:00 on video). So that's the same as the Basic Curry. It's these uses of 1/4 tsp that I first noticed about Syed's dishes. In others, I've mainly seen 1/4 tsp used for garam masala, or maybe other, more pungent / stronger spices such as extra-hot chili powder. It's the subtlety I like.
Don't want to over-analyze. Want to over-eat.
Robbo