Earlier quoted context omitted.
I think I'm hung up on the same thing, chief. Why per capita per square mile instead of per capita? Why do the miles enter into it? Because of more interactions? I'd like to see just the numbers per capita. I suspect they're fairly close.
Because violent felonies such as homicide proximity is the requisite factor in victimhood. ie The victim must be located near the killer. Given 1 homicide in 100k for 100sq miles called "rural" vs 1 homicide in 100k for 5 sq miles called "urban", your odds of being in proximity of a homicide are much higher in the urban area. 20 times more likely.
This doesn't stand up. Crime statistics are measured after the crimes happen; whatever effect might be due to proximity has already taken place.
Consider: in your example you say two places have equal per-capita homicide rates but one is 20x denser. It follows that the denser area will have 20x more people "in proximity" to any given homicide, and therefore that P(victim|proximity) must be 20x lower compared to the rural place.
The way you've done the math only makes sense if everyone "in proximity" of a homicide was equally likely to be a victim, but given equal per-capita rates that can't be the case.