The four lands as a concept has no base whatsoever in the canon of Inuyasha. That is why there is so much variation: the division of lands is fully up to the writer of the fic who uses them in their story.
I mean the more you stare at the map of Japan the less the compass point division makes sense anyway since Japan is situated on a north-east to south-west axel so that the southernmost bit is also furthest to the west and the northernmost bit furthest to the east so any kind of clean division would be difficult.
Also I really want to know what map those people are using who are putting Edo into West because it is definitely in the east. I mean Tokyo literally means 'eastern capital'.
Personally, when using the four lands in Chain I think I divided them more or less by using the islands since they impose natural geographical borders. Kyuushuu and Shikoku were southern lands, Hokkaidou was north, and Honshuu was split into east and west. Of course the problem with this kind of division is that the lands won't be of equal size; east and west would be considerably larger than north or south.
But basically the division could be different in each story you read, because the fic writer is the one who gets to decide how the lands are situated.