H.
I agree - you need to stick with the formula. Perhaps the amount will drop a bit, but he needs it until he's 12 months. You might consider taking advantage of a reduced interest in the bottle and offer him milk in a sippy cup at meals which may help him to get a bit more even if he drops a bottle feed. It will help him learn to use the sippy and may help when it's time to wean from the bottle - he'll already be used to a cup.