The first 2 years I had an ACA policy (2014 and 2015), I was unable to receive an advance ACA subsidy via a premium reduction. This was because my state (a state-run website) at the time wasn't able to understand how I could be eligible for one even though all of my income was investment income and under the threshold. When I completed Form 8962, I was able to take the full calculated subsidy as a tax credit.
But when I changed insurance companies starting in 2016, they were somehow able to apply my subsidy as an advance premium credit. When tax time came around, only the difference between the advance premium credit and the calculated subsidy was available to use as a tax credit. A few years, the advanced premium credit was greater than the calculated subsidy, so I had to give a few dollars back. And in 2017 (and for 2018, I already know), I will go over the so-called ACA subsidy cliff where I will have to return the entire amount of the subsidy as part of my April tax payment. For 2019, I won't even get any advanced premium subsidy, so I will be back where I was in 2014 and 2015 if I happen to avoid the cliff next year.