For any amount, if it's counted as income before the means tested programs, you'll displace many means tested programs for some people. Of course, that also means that those people would likely be made worse off in the short term. Hopefully they could put whatever time they'd spent complying with those means tested programs to better use, and hopefully the other side of the discontinuities in pay-to-takehome would be a little more within reach. I've no idea what it all nets out to...

Right, but given the justification for UBI, you don't want to displace some means-tested programs for some people, you want to completely replace at least one existing means-tested program.

Slight adjustments in the number of beneficiaries doesn't really get you much benefit in terms of eliminating the inefficiencies of existing programs (in done ways out actually exaggerated them since there is a fixed component of the overhead costs for each program.) The real efficiencies Congress when you are able to eliminate programs altogether.

You miss some of the benefit, to be sure, but you also reduce the risks. $100 probably doesn't make much sense as the long term goal for a UBI, but it might well be a good place to transition through.

One benefit of that kind of ramp up is that it naturally phases out existing programs, making them easier to kill when their time comes (and much clearer when their time has come).

It also means (to the risk point above) that if we discover some ruinous dynamic caused by the UBI, we can more easily scrap it and fall back on existing systems.