Long story short, it is likely that if 4.25% of your household income exceeds the total SLCSP premium for the year, no advanced premium tax credit is owed even with the alternate calculation.
After taking a closer look at the calculation, it appears that the alternate calculation is based on half your household income for the pre-marriage months. It is not based on who earned it. Your tax household size is also reduced by one and the monthly contribution amount is recalculated based on half your household's income and your tax household size without your spouse.
If your household income is large enough that your monthly contribution amount based on this calculation exceeds the SLCSP premium, the entire amount of premium tax credit received would have to be refunded.
If your income is 401% above the federal poverty level, based on household size then 8.5% of your income is the monthly contribution amount. If your total income was more than 401% for a tax household of 2, half your family's income may still be 401% for a household of one. At that point, if 8.5% of half your income, or 4.25% of your total income exceeds the total SLCSP premiums for the year, no premium tax credit is owed and the entire advanced amount received must be paid back, even using the alternate calculation.
