FYI-- Everyone needs to find a humidity the works in their own specific environment and incubator. TIme of year effects my humidity levels--humid summer weather brought a drop in hatching%. Because I was not looking at the eggs, the aircells actually.
Development of the air cell to the proper size is the key. Humidity is managed to that goal. Do you have a diagram to compare to while candling?
Search on the 'net using key words: air cells day 7,14, and 18 and you will find a number of diagrams. Pick one that is easy to print and understand for you. Some are black and white, others are colored.. Use it while candling. Hold the egg near it and compare.
For candling--use any small LED flashlight. If you can see the veins, then that flash light is more than good enough to see the air cell development.
Adjust the humidity to make the air cell grow faster, or to slow down development. THere is an optimal moisture loss for eggs; too much or too little , it won't hatch.
By far, the biggest problem is not enough air cell development. You can stop the drying of the eggs but you can not speed up the loss of moisture very well once you are headed into lockdown.
ANy questions? Let me know . . .