Yes, 12-20 is great, although it is a large window, isn't it! Anything less than 12 and they won't be getting the needed calcium and other needed elements from the dairy, and anything more than 20 and they will be too full from the milk and not hungry enough to eat other required foods/calories, etc.
DS was on 16 ounces until about a month ago - 8oz bottle in the morning and 8oz bottle before bed, and then slowly over this month he has been willing to take his milk in a sippy and not a bottle (sigh of relief, was a long process!) and has weaned himself off of two large milk "feeds" and into drinking milk as a drink through the day. I have read in a few places that after 12 mos, large volumes of milk should be discouraged and instead milk should be offered through the day and/or with meals as a drink but, as I said, it took us a while to get there! Now I give him a sippy cup of milk with his three meals, and let him toddle around the house with it while he is playing until it's either finished or it's been about an hour or so. If he doesn't drink it in the hour then out it goes anyway! He isn't really interested in bedtime milk this week, but I do offer a couple of ounces while he is reading his stories if he has not really had enough during the day.
The other thing to keep in mind is that there is nothing in milk that is not in yogurt or cheese. I have a feeling that I have ready somewhere that 1oz of yogurt = 1oz of milk and 1oz of a hard cheese like cheddar = 1.5 ounces of milk but I could be wrong. DH has been pestering me to find out for a couple of weeks now so I may look for the book where I have read that (believe one of my toddler nutrition books) and will post if I can find out. So, if your LO doesn't want to drink milk, cheese and yogurt is a fine "replacement" - and on days when DS is not drinking much (he's been anti liquids the past couple of days with teething) I try NOT to give him his full dairy requirement in milk because I want him to be thirsty enough for water, and so I up his cheese and yogurt instead, and encourage him to drink water. I don't know if there is any benefit in me doing that at all, though!
HTH!