I replaced Swiftarrow Helm, ilvl 187, with Deadly Gladiator's Chain HelmDeadly Gladiator's Chain Helm, ilvl 213, and my score went down to 1687 from 1722. Both are PvP. Both have crit.; Resil.; Ap. with the Deadly Gladiators being higher. Both have Arcanum of Torment enchant. Only the Deadly Gladiators Helm has sockets for gems (1 meta, 1 red. Both equipt.)
Also why is it on every other sight that gives a gear score yours is the ONLY one where my score went down, not up?
Your wow hero score is currently 1800, so I imagine, given the fact that it has only been a day, that you either got a new piece of gear recently or it was fixed...
Empty sockets are a factor. I see this behavior if I equip new gear before I log off and plan to spend the time enchanting/gemming before the next raid instead of before bed.