What a fun game! I notice that I'm somewhat confused, too. I see a couple of different approaches; maybe some of the upvoters would step in and explain themselves.

If getting upvotes for a comment here is something that would confuses you then you aren't supposed to make the comment. The point is to make comments that you predict others will disagree/upvote despite you actually believing what you are saying.

Your confidence is much higher than marchdown's. You should have upvoted because you think he's underconfident.

Even when using 80% as Marchdown's confidence, I didn't feel that our confidences were much different, so I just calculated: the ln of our odds ratio is 1.56, whereas in the original rules, that for

If they're at 99.9% and you're at 99.5%, it could go either way.

is 1.61. So at least according to the OP, I could have downvoted (and I did).

But the other reason I thought our confidences were similar is that Marchdown put >80%, which I took to mean that eir confidence is greater than 80%.