If you modify the tax family size on Form 8962, you will see the following message en route to e-filing the return:
This situation must be filed on a paper return
You are overriding the Family Size total for Form 8962, Premium Tax Credit. For this reason, you cannot file this return electronically. You will need to complete a paper return and mail it in.
In Form 8962, the tax family consists of everyone listed in the personal information section of the return, i.e., the taxpayer, spouse, and any dependents. This is true irrespective of how many of these individuals are covered under a marketplace insurance policy. The tax family size is one of the elements used in calculating the taxpayer's allowable premium tax credit.
The tax family size rarely needs adjusting, and is never adjusted based simply on who's covered and who's not, but if it is adjusted you will not be able to file the return electronically.
Additional Information: