Well, after doing some research, I feel that I know less now than when I started.
After searching for information on optimal Rh for temperature, I found this chart on several sites:
This would seem to directly contradict my earlier comment about lowering Rh as you lower temperature. (I can’t recall where I originally heard this rule of thumb. I watched a lot of YouTube videos, and searched a lot of forums when I set up my first humidor.) As air temperature decreases, the amount of water vapor it can hold also decreases. Rh is an expression of the percentage of the maximum amount of water vapor that can be held at a given temperature, so the amount of water vapor in your humidor at 70%/70 degrees at 65 degrees would be 83% Rh. What I think this chart is then saying is that to keep the same amount of actual moisture in your humidor, as temperature decreases you need to up the Rh. These numbers get kind of wacko real quick. If you stored your cigars at 60 degrees, you’d have to have near 100% humidity. No one in their right mind would do that.
What that chart doesn’t account for, and more to the OP’s issue, is mold. While looking for info on how temperature and humidity affects mold growth, I found another chart:
Now this chart deals with mold growth in a home, and I don’t know how different it would be from mold on a cigar in a humidor, but I think they are somewhat similar. If you look at the chart for 65 degrees, at the 82 Rh the previous chart recommended, you could expect mold growth in 10 days. Now, at 65/65, or even 65/70, there is no risk. Interestingly at 70/70 you can expect mold growth in 163 days.
If you want to dive deeper into the world of science, humidity, & temperature, I would suggest you read this thread:
http://www.botl.org/threads/temperature-vs-rh.80264/
Look, after going through all this, I’m going to continue to keep my cigars at 65 degrees to keep beetles from hatching, and 65 Rh to keep mold from growing. They smoke excellently at those settings, and that’s really all that matters. You should keep yours at whatever setting you like as well.