I have a current set containing 4 Reeves and 4 Swinhoes. The Reeves are 16 days in and the Swinhoe 14. I haven't been paying attention to air cell size since I have automated everything (yeah, I know...) I've been keeping the humidity set st about 56 RH as I've read, with the temp averaging 99.5. The air cells are TINY! I just reduced the RH to 40 and took some photos. Any suggestions would be appreciated to save this relatively expensive set!
I agree with @juliasflock, drop the humidity down low low until lockdown, then candle the eggs to see if the aircells have grown. Adjust humidity for lockdown accordingly. You can try adding a cup of rice to your bator to reduce humidity.