IMO I don't think it matters whether it's 1 Post or 4 posts by what the OP is saying and the types of prizes available (nic level).
So I'm pretty sure the OP will put everyone's name that has listed 0mg into one basket and random draw, then moves to the next one - 3mg, he/she will put everyone that has listed 3mg into another basket and random generate, same goes with 6mg and 12mg. If you did not list it in your post, you won't be included in that draw. Best chance is to include all 4 to have 4 chances like what the OP said.
That's how I've read and interpret what's going on around here lol
I'll leave it to the OP to confirm
@StanSerous