Is it just me or is it impossible to mimic (and therefore test the psychology) of the real impact of UBI unless you implement it across a nation-state. For exam

Is it just me or is it impossible to mimic (and therefore test the psychology) of the real impact of UBI unless you implement it across a nation-state. For example, let's say you test in a small town in Minnesota. It's impossible to rule out variables such as federal taxes, healthcare costs, mobility, etc. I therefore think its impossible to test UBI on the scale of the US for example.