After reading all the replies from everyone, and further read the tax code, I came to the conclusion that

the government doesn't want you to double dip.  It means if the taxable income is greater than the capital gains, you have zero to multiply by the 20%.  My client's situation is just that, i.e. $700K in taxable income and $900K in capital gains.

Thank you all.  I think we found our answer.  Bummer but that's the law.