Canada

No need. Interest and penalties on the unpaid taxes amount to significantly more than the float.

Hmm. Perhaps your right. I just dislike the idea of a rich dude essentially getting a loan from the gov't by refusing to pay his share upfront. But if the math works out and it doesn't hurt fundability then I'm sold.

UBI should be treated more like a dividend paid to a shareholder. The shareholder’s financial situation is irrelevant to what the shareholder is owed.

This is tied to the "entitlement vs charity" concept. So agreed on that point.

However, I also wrote earlier that,

Basically the rich are required to pay as part of their tax their own BI in advance, before the govt doles it back out to them.

Solely for that purpose the financial situation is kinda relevant. The rich, and perhaps the really high middle class, effectively have to self-fund their own UBI. Everyone else has it funded through a pool of money that the gov't provides (which in turn comes from the usual taxation authority, including taxes on the rich).

As a concept, this shouldn't be important to the ideal that is UBI. However, it's an important wonky implementation detail - everyone still gets UBI and it's still an entitlement not a charity, but this detail makes it affordable for governments to provide (the rich technically get it too, but it's basically just an accounting gimmick).