> The big question for me is how would the introduction of UBI ultimately affect that ratio, given that you would be less disincentivized to stay with the underproducing group?

The “given” is backwards. Compared to existing means-tested welfare systems, UBI funded by additional high-end taxes provides less disincentive to move out of the underproducing group.

If the minimum support level provided by UBI is used (in whole or in part) to offset and reduce minimum wage, it also reduces the barriers to people moving immediately to a less-inderprodicing level, and eventually up and out of the underproducing group.