Anyone who works for the government (including teaching & military) with retirement benefits is not going to subsist on just UBI once they stop working.
That does meet my bar of "unreasonable".
Mathematically, that makes no sense.
You are confusing "federal taxes" with "federal income taxes" and assuming the only way to increase the latter is to multiply the existing marginal rates without changing the structure; since a one portion of the drive for UBI is to address concentration of returns in high-end income and capital gains, the natural first thing to do is to uncap payroll/self-employment taxes and tax capital income the same as labor income (both the taxes on labor income styled as "income tax" and those styled as "payroll tax". That -- alone -- more than doubles taxes on long-term capital gains.)
There's also other income that excluded from taxation or taxed favorably that is concentrated at the high-end that could be targetted.
This whole theory hinges on automation taking a significant bite out of the workforce, which will raise profits in direct proportion to lower costs. If companies aren't paying their employees anymore, a portion of their proceeds should go to paying back society as a whole - after all, if there's nobody to buy their product then they are dead as a company.
If 40% end up unemployed as a result of automation, then there should be a significant increase in new jobs in the automation industry.
The solution is retraining programs. Paying displaced workers UBI while they're retraining is a compassionate temporary solution, but not long-term.
This doesn't actually fit very well with the conceptual basis of UBI as a replacement for means-tested benefit programs, as defined-benefit pensions are not means-tested benefits.
Though its true that a number (though not all) UBI proponents have either explicitly called for replacing existing Social Security-style retirement programs, or implicitly suggested that by including the existing cost of those programs as funds available for UBI.
(The US has very few real pension programs any more, since the 401(k) and IRA systems were put into effect and displaced them.)