I don't understand what you mean by this. UBI redistributes income - wouldn't it obviously be funded via taxation? USA would be able to afford a much higher UBI than Sierra Leone would because US income is higher. What determines how much UBI can be issued if aggregate income is irrelevant?
If you fund by a 100% income tax, everyone would quit instantly. There would literally be no point in working for money. UBI cannot be funded by the thing UBI would eliminate.