I grew the vast majority of my garlics (I usually planted 12-15 varieties each year) in the ground, but also grew it in large, 24" pots. I generally planted 6-8 cloves per pot. All my garlics performed about the same regardless of whether it was pot grown or in-ground grown. I typically planted my cloves in mid-October, Anya, so if anything, you are planting too late, certainly not too early. I was in NE Mississippi, with a far different climate than you in NY. Your first frost date is probably a month before mine. I would suggest planting your cloves in mid-September, but that's only a guess.
You might wait a couple of weeks to pull your garlic, but the size probably isn't going to be much larger. You certainly don't want to fertilize now. Were your garlic plants growing in full sun? They should be.
