I think his comments on the SCOTUS ruling and his change of labels is appropriate.
If I were him and asked the same question about Romneycare, I’d focus on it along the lines of “if a court says it’s a tax, I’ll say it’s a tax. But no court has ruled on it.”
He loses either way because he passed and defended the same thing in MA. So he ends up with :”It's a tax under Obama and a fine under me”
If Romney could say :”We tried Obama-care in MA and it worked out terrible so I know first hand that we must repeal it” at least some would believe he is serious, but that would cause him problems too.
Personally I think the fine-tax debate is silly one to be having.