An update after I finally had an opportunity to cook with this base. Firstly, the additional water / stock I added to achieve oil separation was very noticeable in the base, and in retrospect was a mistake. The first curry I cooked, SnS Madras w/chicken, was watery to taste, so before it left the pan I did several extra rounds of base addition and cook down to remove that extra water. This was a satisfactory fix and I cooked 2 nice curries, but it is a pain in terms of extra time. DO NOT add the extra water to this base just to achieve oil seperation. Cook the base to specification and use it as is. Plenty of oil comes out of it in the final dish as expected. I may experiment without the potato to see if this is the culprit.
In saying this though, I don't think the base was the only issue with the Madras, which was lacking in depth and richness. It is a very basic and easy recipe to follow but I found the amount of tomato puree, further diluted 3:1 with water, was too weak. I ended up adding extra tomato "paste", until I was happy with the amount of flavour. I didn't have the same problem with the Chicken Ceylon I cooked afterwards so it wasn't just the water in the base. This is a geographical issue with naming.
What British recipes call Tomato Puree is called Tomato Paste in Australia. So here's the tip for the new Aussie members. Tomato Puree is Paste. Out here Tomato Puree is simply pureed tomato or Passata. Triple concentrated tomato is called paste.
In the end I achieved 2 very nice curries but it wasn't without extra work. An inexperienced cook would wonder what they did wrong.