I'v always had trouble getting RH up in mine too. High 30's is about it with water trays full and vent open at all. I moved all eggs to hatcher today, closed the vent all the way after reading your post. It hit 55% and holding with both trays full of water but no eggs in at all... I think this is a indication mine may not be as air tight as some....I run the vent where it needs to be to get the RH needed and dont worry it too much. killer little bator. I load eggs in the morning. Bill
If you cant keep the humidity up to 40ish without the vent pinched down. I say its sucking more air around cracks than others. In turn humidity is lost with air exchange. If air is exchanged this much, plenty to hatch eggs in...
So short answer to your question, yes I think its fine.
This will be the 5 batch I'v ran thru mine and all have been in the 60%+ range for hatch rate.