UBI is always going to have a de facto cutoff where some people pay more in tax than they receive in UBI (unless your government is funding it solely by money printing or having massive amounts of oil per head of population).
The only question is what that level is at and how steeply the relevant taxes reduce turn its net benefit to a net cost, and that's something governments determine just like the tapering on any other form of benefit.
UBI is always going to have a de facto cutoff where some people pay more in tax than they receive in UBI
That's not a cutoff; it's a continuous function that crosses zero at some point. With a UBI funded by an income tax you're never worse off earning more.
> With a UBI funded by an income tax you're never worse off earning more.
Provided you can earn more without putting in any more effort; otherwise marginal effort eventually exceeds marginal net income, and the income tax shifts that crossover point toward a lower income where the effort remains worthwhile.
A smooth transition out is more or less by definition not a cutoff (a cutoff being a sudden thing). This is an important distinction, because it means it's never harmful to earn another dollar.
Since we don't have a wealth tax, there isn't even a smooth transition out along the dimension that the article discusses.
The article also discusses and criticises a 50% effective marginal tax on working which is absolutely how an UBI smoothly transitions if funded by an income tax, and in theory the taper could be steeper still. Not harmful to earn another dollar, but not especially lucrative either.
Nothing about a UBI prevents it from being coupled with a wealth tax (possibly even a regressive one which kicks in at low levels so recipients are disincentivised to save) if the government wishes to fund it that way... and they'll need to find additional funds from somewhere.
The only difference with UBI is the subsidy itself is a lot less targeted than "financial aid for registered disabled people", so the government has to find a lot more ways to claw it back from some sections of the population. That can be sneaky and regressive, just like a non-universal income only disabled people are entitled to can be completely without income and wealth qualifications if a government wants.
The only question is what that level is at and how steeply the relevant taxes reduce turn its net benefit to a net cost, and that's something governments determine just like the tapering on any other form of benefit.