I mean it’s pretty subjective as everyone has different tastes, and it was also dependent on the encapsulated acid as some were definitely a bit more potent but luckily they are both powders, so it is very easy to make samples.
Just a bunch small cups and do an increasing ratio from 10% acid to say, 50% acid, and see how they taste to you. Easy experiment to do that doesn’t involve using product and let’s you get an understanding of how the sugar/acid coating would taste on its own. There will definitely be some slight changes when you introduce the candy, but for all intents and purposes, this would give you a solid foundation.
I think I was normally using somewhere between a 70/30 to an 85/15 (sugar/encapsulated acid) so that’s probably not a bad place to start but YMMV depending on what candy it ends up going on and how the sour/tart coating meshes with the candy product.