My two cents...
I’ve been mixing about 4.5 years. Everything is a test, until I’ve made it more than once, successfully, and it’s been fully steeped ( however long that may be for each juice, maybe a week, maybe three months).
My first test, I do 10 mls and use half as much flavor as I think it’ll need. Even though I’m quite familiar with most of the flavors on their own, and in recipes I make often, it still pays to be frugal. No telling how each will work with different combinations until I’ve tried it. And it’s easier to add more than to dilute, plus, starting low is the only way to be sure not to over flavor.
I don’t want to use more than I have to, although I like a huge flavor.
You may well like and need 20%, no law against that, but if you start there, you won’t know if less would have done it.