One of my barbecue Aha! moments was reading Paul Kirk's Championship Barbecue Sauces. I read this book after about 2 years of owning my own smoker. A lot of things he said about building your own bbq rub clicked for me as he obliquely addressed the range of ratios of spices in a rub. As I recall, he was using a certain amount of paprika as the rub "base" and adding things to it. Saying things like that much paprika can take up to X amount of garlic powder and so on.
He wasn't clearly setting forthing ratios, but the info was there.
I've never encountered that sort of discussion anywhere else again in BBQ books. And it's something I really want to understand better.
Sadly, he didn't do as well with that concept in the sauces section.
While my question could lead to a whole big book itself, I'd like a rundown of your personal flavor theory as it pertains to building rubs and barbecue sauces.