Sometimes you have a microclimate that allows you to grow some onions better than others. Sometimes you just have to experiment to see what works out.
I don't have a lot of space for onions and I only grow a few just enough to last about a month.
My biggest problem is the curing and storage. They are harvested when it is getting warmer. We don't have root cellars here and when they are left out even in the patio, onions that start out sweet end up quite pungent after a couple of weeks. I don't really know how to change that. In May-June, it is humid with the temps in the mid 80's.