Sorry Bob, what I meant is that unless you know he's on the same pressure as you (and that he's set his altimeter correctly!), his being at 2.5 doesn't necessarily mean he's 200' above your level.
I should perhaps have said "rely" rather than "fixate"!
I would guess that any investigation would at best conclude "late sighting" by one or both pilots.
BTW, further to what Shy said, when I was flying in the States there was an "Operation Lights On" campaign, basically aimed at small aircraft in a busy environment. The gist was an encouragement to fly (during daylight) with landing lights and strobes (if fitted) on, making yourself that much more visible.
ap