But if the first difference is much bigger than the second, the pattern is the reverse.

It's not literally the reverse, because if you don't create those FAIs, nobody will, and so the UFAIs won't have the incentive to give you your small share. It's never good to increase probability of UFAI at the expense of probability of FAI. I'm not sure whether there is any policy guideline suggested by these considerations, conditional on the pattern in utility you discuss. What should we do differently depending on how much we value small vs. large control? It's still clearly preferable to have UFAI to having no future AI, and to have FAI to having UFAI, in both cases.