I think $1k does count as sufficient for basic needs, personally.
I think part of the problem is that people are assuming that you can and should pick a number for UBI that is sufficient for basic needs everywhere.
$1k/mo is probably not enough in San Francisco. But should our UBI be set up to allow anyone to meet their basic needs anywhere they'd like to live, or should it be set up to allow anyone to meet their basic needs if they're willing to leave the high cost of living areas and go out into the rest of the country where rent and food and transportation is cheaper?
Also a UBI shouldn't have to facilitate living _everywhere_. Santa Monica is lovely. Should we arrange it so anyone can move to Santa Monica and be able to live there fully supported on their UBI?
I hadn't really thought about transportation costs, and am inclined to leave it out of UBI calculations as it doesn't feel like a necessity. But in a rural area transportation is necessary just to buy food, so I guess that adds some complexity.
For a living situation "basic" implies a shared space (family or otherwise). For food it would imply enough food to be healthy, but nothing about the form of food.
I think $1000/month/person probably is "basic" income. You can survive on that indefinitely.
(Healthcare is the other big expense, but I don't think UBI can reasonably cover healthcare, it's to complex and variable)