When I tested my incubator before my first attempt, I discovered that it ran at about 21% RH when dry, and bumped all the way up to around 75% with a little water added (in the recommended way). It's crazy that the winter humidity here can be 90% outdoors, while only 30% indoors.
I tried to address these extremes, first by keeping it dry for a a few days, and then adding the water (which fully evaporated in 3 days), hoping for a reasonable average RH over time. Later, I tried adding little jar lids of water rather that the full reservoir to reduce the surface area of water, hoping for a lower high RH. That worked.
Sorry I'm not really answering your question because I'm new to this, but these are a couple options for playing with your levels.