OK, so there are classes of activity that are fairly inelastic, but not as inelastic as those requiring use of land. Fair enough. But why would the cost of air travel not increase in response to UBI? It's not inelastic, but modest increases don't appear to reduce demand much at all. Or eggs (again, not inelastic, but not very elastic either)?

The housing:land demand ratio is also not fixed, due to multi-level dwellings (hence, for example, Singapore or Hong Kong), or increased density (e.g. ADUs or smaller lots).

I just don't see why you see UBI only affecting owners of a nearly-inelastic resource (land) rather than everything else too (even if to a lesser degree) ?

It would increase those prices! But that would then incentivize additional production, which would drive prices back down close to each good’s cost of production (modulo the suppliers’ dominance and ability to demand margin).

So same mechanism applies to land, except then there’s no way to spur additional production of land, so the price just goes up.

Re density etc: correct, which is why I’m not arguing this benefits homeowners or building owners, except to the degree they are also landowners. A building owner who does not own the land underneath his building would not benefit much, the person who he pays land rent to will capture nearly all of the upside.