A lot of positive externalities that UBI will bring simply won't kick in at low payout levels, whereas the negatives which will be brought in by diversion of funds will be apparent.
The externalities I am talking about are of this form: -Increased benefits to public health as people are less stressed about losing jobs -Increased entrepreneurship and all the benefits that come from it -Increased cultural output and the increased geopolitical influence
The whole point of UBI is that's it's not another handout.
It's giving everyone an option to not have to work a day job to survive (something that moderately well-off people, or people with upper-middle-class parents already have).
The impact of "what if most of the citizens didn't have to work to survive" can't be estimated with a small hand-out, because it will not achieve that.
In other words, UBI is somewhat binary in nature: either you have it, or you don't. It doesn't scale down beyond a certain point.
