How does Drop Rate Potential stack with other forms of Drop Rate?

Going off how (I think?) other potentials work, I have been assuming drop rate gears are additive and then that total is multiplicative with card + buff + event.

2[card] * (1+0.2+0.2+... etc)[drop gear] * 2[event] * 2[buff]

I was thinking that as another alternative as well but it still seems a bit ridiculous to me. I have 7 sources of 20% drop rate, so if I were to use this formula, I would be at 19.2x drop rate. If it's just 2*2*2+(0.2*7) then I'm only at 9.4x drop, which seems a bit more realistic. If it's all multiplicative, then I'm at like 28x drop, which is just... stupid.