I think you should think of UBI not as "everyone gets $X more" but rather a redistribution of income. The lower half of income earners will in sum receive more than currently while the upper half will have less due to higher taxes.
Sure, but generally the top income earners aren't really in the same market as people with lower incomes. Sure there's indirect impacts, but the housing stock that they pursue is different, they eat at different places, probably shop at different grocery stores... the impact that this will have on their spending will be substantially more muted and difficult to measure in a model as compared to the impact of everyone at (lower income bracket) receiving an increase to their income.