Not familiar with GAI. Do you mean AGI? If so, that is not the number you use. It's "Total Income", but sometimes its the same number. If your past three tax returns show plenty of total income, you can qualify on income. You are a self employed "investor". Consular Officers tend to believe that if you are willing to report the income and pay taxes on it, you actually earned it. Even so, it is helpful to show you own the underlying capital too. That's just part of the picture to enhance what they see as the totality of circumstances.
As kind of an aside, your parents' decision is WHY it is so important to show you own the assets involved. Many parent or other joint sponsors would rather loan you the cash to qualify than sign the contract in the affidavit of support. Showing you've owned the assets for over a year, takes that suspicion out of their minds. But, if those assets are how you're producing the taxable capital gains, then that solves the problem too. If you can show transactions in your name, that will probably do.