Does this really solve the problem though? What happens if someone 3 miles away is talking to someone who's 1 mile away from themselves, but 4 miles away from you? Then you'd see the transparent text of them talking to some person you can't see messages from, yet also see transparent text of them responding to people you can see messages from.
I personally don't see how you could completely avoid this without some kind of fixed regions, unless you required people to do some kind of an "@user Hey..." for every message so that you would know if you share the same sphere with the destination user. This makes it more tedious and less fun, though, plus it takes away the whole idea of multicasting.
I personally don't see how you could completely avoid this without some kind of fixed regions, unless you required people to do some kind of an "@user Hey..." for every message so that you would know if you share the same sphere with the destination user. This makes it more tedious and less fun, though, plus it takes away the whole idea of multicasting.