Yes - because if they were receiving FT NMW, they'd still be worse off than non disabled people earning FT NMW.
That's the point - to ensure nobody is disadvantaged due to the extra costs of their disability.
Having a maximum of FT NMW as income;
Person A income (disabled, could be working PT or FT or not at all) 15,000 (for example).
Costs of disability -5,000.
Net income 10,000
Person B income (not disabled) 15,000.
Costs of disability 0 as they are not disabled.
Net income 15,000
Preferred situation - the one for equality rather than deliberately ensuring that no disabled person can ever be in the same position as the theoretical 'higher valued' non disabled person;
Person A income 15,000
Costs of disability -5,000
Additional income to account for costs of disability 5,000
Net income 15,000
There is, as a result, an incentive for the disabled person to work if they are able to, as they are not penalised by having 5k of unmet costs meaning their standard of living/income can never be as good as somebody who is not disabled. They are actually, for a change, treated fairly and put in the same position financially as somebody who does not have to spend an additional five grand on simply being able to get themselves up, washed, dressed, travel to work, work, come home, shop, cook, clean, medicated, etc.