So LHR-BOS on a A380 automatically isn't Long Haul, similarly JFK-LHR on a 787?
I really don't know why some insist on pigeon holing flights into categories like this but do I know some love the idea they've done "Ultra Longhaul" so maybe it's associated with that thinking..
I know some on-line sources insist Longhaul starts at 6 hours, ultra at 14....but that's on-line.
In the real world a Longhaul crew looking at a mid-winter with the jet stream fast BOS-LHR, of say 5 hrs 55 min gate to gate don't turn round at briefing and say "OK folks, we are shorthaul tonight".
Similarly a Longhaul crew looking at a mid-winter against the jetstreams SIN-LHR that could be > 14 hours don't suddenly start thinking "ah, get the books out, we're ultra longhaul on this one .."
Most places they'd be operating both sectors under Longhaul rules and procedures.
FWIW and as a BTW the seemingly much loved Ultra category, when relevant, is nothing to do with passengers, it to do with crew rest and scheduling
I reckon one of the metrics worth considering as a passenger, if you have to use labels:
Time to watch one average feature length film or less: Shorthaul.
Time to watch one, maybe two films - long shorthaul drifting towards short Longhaul.
Time to watch two films or more - Longhaul.
Anything else is really mainly something for the schedulers (e.g. Ultra) and accountants (e.g. Mid-haul) to concern themselves with.