Blip, I'm a tower controller with a (non-current) area rating. Spoken to a few pilot friends and this has come up a few times. On exact reciprocal routes, or same direction routes, using gps, the passing of another a/c below occurs with sufficient accuracy that the radio altimeter notes the passage.
So, not speaking for other nav systems, or crossing routes, but a few of the guys I know have said they always offset 200metres right. (Maybe 100,maybe 250, can't remember, but it was something like that.) Why right? Common sense. Rules of the air=keep right. Nobody is fooling themselves it's a separation standard; it's simply a mechanism to hugely reduce the chance of a meeting of metal on exact recip routes should for any reason the vertical space be zero.
ATC is not going to notice it on the displays.
ATC is not authorised to approve it, either, so I would imagine most of us would be happy not to officially know it's being done.
One of those things that seems to make sense. (For this specific case.) I don't know of a procedure or separation standard that would be invalidated by flying 200metres offset. But .9 of a mile....?
Best bet I reckon is to go through your union technical rep to try and get an approval effected with regulatory blessing. Otherwise, one day, the holes will line up in another way, and although pure bad luck, that being 200m off track might just be enough to cause the midair, and guess what they'd say then.