Well Finn won't be pushed on anything either really...he will just refuse to drink it and toss it aside. So I am torn between leaving it in the bottle and hoping he'll just grow out of it or making a really good solid effort to offer and get him on a cup. I guess at the end of the day he won't learn to use a cup unless he's offered a cup repeatedly - sippy cup, straw cup, whatever doesn't matter.
We are doing the same as you, putting after meals, a few ounces in his straw sippy, he seems to do better with that kind of cup. Then when he kicks up his fuss about wanting his bottle (which we know the clear signs of now), we just transfer it and give him the rest. Daycare gives him the lunchtime bottle, we only send 5 oz but they top it up because he's not eating food. She said to me the other day 'well it's only milk' which made me feel bad about saying to limit the amount. I want to limit the amount because it fills him up and he isn't hungry.
He's also getting a D supplement in his bedtime bottle so hopefully that takes care of that.