EIC disabled adult child

I am filing as Head of Household. I have a 21-year-old son who is permanently and totally disabled.

​According to IRS Publication 596, a disabled child of any age is a 'Qualifying Child' for the Earned Income Tax Credit (EITC). 

​My issue is that TurboTax is only giving me $1,983 in EITC, which is the amount for a person with no children. Based on my income, having one 'Qualifying Child' should increase my EITC to over $4,000. The software is not 'bridging' his disability status to the EITC calculation. I have the disability box checked, the support box set to 'No,' and the residency set to 'Whole Year,' but the software is not generating Schedule EIC. I need to know what specific back-end question is blocking him from being a Qualifying Child.