You basically say that the how-factor is something specific, namely a very small amount of balefire. RJ said, though, that in this case - namely if a very small amount of balefire is used - the DO can still transmigrate a person anywhere, without any additional restriction that this would also only work close to SG.

Then you say that the where-factor is basically not a specific location, because it doesn't matter if Asmo had died in Caemlyn, in Emond's Field, in Cairhien, Tear or in almost all other places on the world, because the DO could only transmigrate Asmo close to SG, though it's clear that he wasn't there. Thus, the specific where-factor doesn't really make sense.

However, we know from BS that there are special circumstances of death (except for the whole balefire issue), which prevent a transmigration, but he doesn't want to reveal them yet. This could very well be linked to Asmo's death, whose concrete circumstances are also not revealed yet.

Besides that, if this were the revelation, the killer had to tell the readers, that he/she precisely used a very small amount of balefire, which normally could lead to a transmigration, but in this case it didn't matter, since it was too far away from SG. Such a revelation would seems pretty awkward, and I think it's unrealistic that a killer would muse about these academic questions concerning balefire.