Is your rule about distances actually a base part of your ethics, or is it a heuristic based on you not having much to do with them?

Its more of a heuristic. Any ethic that used a specific measurement of distance in its raw calculation would be odd. There might somewhere be a line where on one side I might care about a person, and on the other I might not. Where someone could stand on the line exactly. That would be mostly silly.

if you have family in another country you're still invested in what happens to them.

most of my family lives within a few suburbs of me. I have a few cousins who have been living in England for a few years; I barely even know what they are doing with their lives any more. (I wouldn't excommunicate someone for being far away, but I wouldn't try as hard as someone living in the same city as me) My grandmother keeps in touch with the cousins far away but I don't think its a requirement for me to do, and I am sure they also don't feel like they have to keep up with my life either.

Do you care whether the unknown people are suffering more? Mostly because of the unknowns - no. Unknown people are suffering by an unknown amount - without seeking out those unknowns I have no reason to care.

If donating $X does more than donating Y hours of your time, does that concern you?

There is also the case of warm fuzzy utilons; where I can know that my intended impact hit the nail on the head; where I might otherwise find it difficult to know if $X made the intended impact. Its kinda like outsourcing making an impact to someone else in letting them use that $ for what they feel is right. I don't necessarily feel like I can trust others with my effectiveness desires.

Does this make sense? I can try to explain it again if you point out what isn't making sense...