World Quest Rewards' Level

On one toon, the rewards are 445, on another 390. Can anyone explain the discrepancy? Is it your neck level or reputation or something?

It’s your overall item level. The emissary reward will be at or just above your average ilvl, capping at 445. And the reward isn’t guaranteed to replace a weaker item. I’ve had plenty of emissary rewards that were the same slot as my strongest gear.