I have only had success growing globe onions ever winter, so placement vis a vis the drip line is less important if you have wet winters. globe onions can have almost no competition for sun and resources. I grow them in degraded
wood chips only for weed suppression. For that reason I am moving away from large onions and toward wilder-type onions, less of a pain. I'm experimenting with a couple bunch onions this year, but it is a way of using the under-tree area. Daffodils are not very picky. Garlic is pretty picky, grows same as globe onions in my
experience. Same with shallots.
The other issue with growing over winter is if you are anticipating benefits from alliums for say cerculio suppression, you obviously don't get much if they are harvested in the spring. So I'm doing more wild-type under the trees.