I'm certain it's the base, not the curry. The rajver Madras has always turns out a decent effort with every other base I've made.
I think primarily I would use far less spices. I'd also leave out the wierd fancy pants ingredients such as Tamarind paste, star anise etc. I think I'd do a spot of gentle frying before boiling perhaps but I'm not too sure.
I think more and more that a lightly spiced base gives me better results. As long as it has onion, some tomato, garlic and a light spicing of the common ones, it usually comes out fine for me. I'm pretty sure the green pepper doesn't do anything great for me either...
I made another attempt this weekend, which was fantastic! I used loads of oil, some really nice large onions from Sainsburys, fresh tomatos, garlic, ginger and some home ground Garam Masala and some Turmeric. For my Garam Masala I used 1 tsp cumin, 1 tsp Coriander, around 8 green cardomom, 1 black one, a piece of Casia bark, a few cloves and a small piece of Nutmeg. I gently heated around 3-400 ml oil and added the GM, a desert spoon of Turmeric, 4 large onions, 6 fresh Tomatos and cooked until soft. Then I added a litre of so of boiling water and simmer for a half hour then blended. It really is excellent and makes a great Bhuna.