Hi, I always dry hatch now but it is really more like dry incubating. I have found that 20-40% the first 18 days and about 60-70 at lockdown works great out here.
I would aim for 35% but not make yourself stressed over it. The only thing I have noticed (thanks to a friend who keeps good records) is that dry incubated chicks seem a little smaller. They do catch up with the rest over about a four week time. But they are a little smaller.
However, they don't drown after pipping! I like to do lockdown with my plug in to keep the humidity more balanced. I have noticed also that the humidity spikes are what seems to make some of my chicks get "glued" in. Then I have to help them out.
Yesterday and today I have hatched out about 10 chicks mostly silkies using the dry incubation. They hatched a few days early, probably due to me not keeping them cool during storage. Anyway.... I had not added any humidity and they hatched out with no problem, fluffy, dry and healthy at about 30% humidity and that was due to the chicks hatching in there. I wouldn't try this with shipped eggs or precious eggs though