And if someone lives so far away in space or time that just to locate him requires as much information as it would to specify their whole mind starting from a rock, it's not obvious to me that he exists in a sense in which the rock-mind does not.

I intuit that the difference between logical and observational uncertainty could be relevant in non-obvious ways. Anyway, this sort of thinking seems obviously correct, but I fear the comparison may mislead some, considering that inferring the numbers and preferences of minds in causally disconnected parts of the multiverse through sheer logical reasoning is probably way way way easier than interpreting the 'strength'/'existence' and preferences of minds in rocks, at least as I consider it. (I worded that so poorly that it's incoherent as explicitly stated but I think the message is intact.)