I keep my humidity between 40 - 45% and at lockdown it goes all the way up to 65%. . . .
I don't normally have any issues hatching my marans or any other breeds with humidity at these levels.
I tried lower humidity once and ran into problems.. . . . I went back to this and it works for me.
It has got to be a myth that they are harder to hatch! My Maran egg was the only one to hatch this morning out of the 3 that I put in my inexpensive chick bator. He is very healthy and it was a very easy great hatch! The humidity from day 1-18 was 45-50% and the last few days it was 60-65%. It was a late hatch though on day 24, started peeping day 23, before that nothing. I wish you the best with your hatch!!!