That’s why I’m in favor of a straight cash subsidy through the negative income tax.
If you’re receiving $1234/month (typical disability payment from a few years ago), that works out to $14808 annually. Under your scheme, you’d have to find (and work) a job paying $14809/year just to see an increase of $1 in your real income. In effect, you’d be working for a full year and being paid a net of $1.
It is more about ensuring that a person receiving assistance can work as much as they are able without any concerns. Anything less than a totally smooth off-ramp to financial assistance is bound to create scenarios where the optimal strategy for a worker is limit their maximum compensation below the arbitrary financial cliff.