I've seen it explained to me a few times now, but, as Silent_Z said, you multiply all leader skills, add up resistances, then multiply them with the leaderskill. What this means, is that for 100% reduction, you actually need 100% in the resist awakenings. Why? Because you still need to get rid of 100% of whatever is left over from the leaderskill. Basically, the leaderskill component isn't super relevant if you are going for full immunity. On the other hand, if you are OK with going for a minuscule amount of damage, then you can get by with fewer resist awakenings overall.
The reason people like Minerva is that she resists other colors, meaning you will have an easier time stalling for the puppet. As for your Minerva team, right now, you have 16 awakenings before latents, that means you have 80% fire reduction before the leaderskill reduction, so I think you'll take like 5% of damage from fire. However, it will still take the whole 20 fire latents (at 1% each) to get to full immunity.
Currently, I'm planning on trying to get the traditional Minerva cheese team together. As for a dark resist team, I'm going to try Cecil/Dragon/Dragon/Thothdet with like 15 dark latents and something else for a sub (need STRONG dark bind clear for heradra). If I pair with another Cecil, I wouldn't even need the latents, but, ironically, if I pair with R. Hades,I still need them. Otherwise I still take 3.75% dark damage. Since my daughter has a hades, I'm going to plan on the resist latents so we can try to get through heradra together.