Well yes, but Finland wasn't experimenting with basic income for philosophical reasons. They were experimenting because they have high unemployment and a comple

Well yes, but Finland wasn't experimenting with basic income for philosophical reasons. They were experimenting because they have high unemployment and a complex, and expensive, welfare system. So what they wanted to understand was the effect a basic income had on those factors. The next stage of the experiment, that wasn't funded, was to extend the experiment to include the employed. Even there, I would expect they would still focus on low incomes as that's where you would expect to see an effect. To go beyond that, it's not clear what you'd learn without having a very large scale experiment i.e. one that materially affects the level of taxation. I can't imagine they'd be interested in that without seeing a significant, positive effect on the first two categories. And as a side point, I don't believe the idea was ever to test a UBI just a basic income. Unless you're intending to do away with all differentiated welfare, highly unlikely in a social democratic country, the universal bit is probably more harmful than beneficial.