You really have to use a lot of oil, if your recipe says 4 tbsp then thats what to use.
I originally started making curries and thinking" bugger it im not using that much oil" and would use a couple of tsp instead. Not the same thing at all, for one thing you'll burn your spices a lot easier as they dry out and catch.
Also the speed of your cooking effects the oil rising when cooking the base.
Too high a heat and the rolling boil seems to keep remixing the oil back into the base.
well i think so anyway, i go for a low-medium simmer, when making the base.
And on the stirfry stage a medium heat and DONT stir too much once you add your base try and leave it alone for a bit, watch it but leave it.
Before adding the base, mix it as much as you like. Also when you add the base and are in the process of leaving it alone, you might notice that the sauce will stick a little bit around the edges of the pan, so much the better, stir it back in, the curry tastes better. Soon with practice you'll be able to resist the urge to shake and stir and your oil will rise easier.