Keep a bucket of water behind the fan and then you always have water easily available which should keep temperature swings down and humidity up. I would not put strong wind on mine just a light breeze
When did you start yours? I usually shoot for sowing around Jan 10. I’ve found that any earlier is of little benefit for final bulb size.
Last year I started them Feb. 1 and they were a little smaller than I wanted when it was time to plant them out, so this year I did New Year’s day for my first two flats, then the second 2 a few days later. That may be earlier than necessary, but I’ll soon need the room under the lights for other seedlings, so they’ll be spending days outside when it isn’t too cold and then getting just window light on the cold days so that may slow them down.
I’ll adjust next year based on how these do. But I agree that they don’t need to be huge at planting to get big onions. Even though mine were a bit wimpy when I planted last year, I still got nice big onions.
Lee Reich posted about direct sowing in early spring on a recent blog post. He claims they ended up about as big as the onions which were started ahead. It makes some sense to me, there’s probably a fair amount of transplant shock the way we plant out onions. And how else did they get the onions going before grow lights and cheap greenhouses? I’ll probably give this a try at some point.
For me, planting early is pretty much a guarantee of a record freeze ten days later…