If you have hatched LF at this time of year, start with that. I find winter to be dry, and I need to add a little moisture compared to the humid months of summer where I live. I am setting medium eggs, pullet eggs, and I expect to need a little more moisture as smaller eggs lose moisture faster than a larger egg.
Do you have a chart to compare air cell size when you are candling. Try googling." air cell at 7th, 14th and 18th day" you should find a diagram to print off and use for comparison on those same days. THen adjust the moisture levels if necessary. For example, if the air cell is too large, add more water and keep the moisture level a bit higher.