Have you tried throwing in a bit of garlic with that lime zest? I found that a clove or two blended right in makes the paste way more complex. A pinch of sugar can also round out the sharpness from the fish sauce. Letting it sit for a day lets all the flavors really come together. Then it becomes this magic sauce that goes on noodles, grilled meat, even eggs. Once you start tweaking it, you never go back to the jar stuff.