$1000/month is enough to live off in many parts of the United States. I lived off it pretty comfortably a few years ago when I was in college – although I had four roommates, we all had our own rooms.

Obviously, it's not affordable everywhere, but I think incentivizing people to live outside of expensive areas is a good thing (adjusting for cost of living would mostly just funnel the extra money towards landlords, i.e. rent-seekers).

Your denominator is too large. Children would not be receiving UBI, presumably.

Also the numerator could be increased via a wealth tax on the top 0.1% or so.

Bear in mind that an income can go much further when you can invest significant effort in seeing that it goes further.

And certainly, as Zarel says in a neighboring comment, it wouldn't be affordable everywhere to live on just the BI. It doesn't need to be.