Hey @ericvanbuskirk ,
I deal with this as well. The answer is
U.S. citizens living in a foreign country for at least 330 days of a 12-month period are not required to get health insurance coverage for that 12-month period. If you’re uninsured and living abroad under this definition, you qualify for a health insurance exemption. This means you don’t have to pay the fee that other uninsured people must pay.
For your 6-month case, and my 7-month case, I’m 99% certain that means you need to register for ACA in whatever state you more or less arbitrarily choose to reside in during those months.
I have not spoken with a lawyer about this, primarily because the rule seem so similar to the Foreign Earned Income Exemption (feie). I’m assuming they used that tax rule as a model. Obviously, as @wanderingdev references, in order to qualify for either rule you will need to stay out for an additional 5 months. Much easier said than done.
On the opposite end of things, I believe you are allowed 90 contiguous days uninsured without being penalized per year. I can’t find that directly on an ACA website but here it is from another: http://obamacarefacts.com/questions/more-than-90-days-without-coverage-do-i-owe-the-fee/