What do I need to do to earn the tier 6 mission chest reward?

I've noticed that no matter how well my team and I have done in missions so far, we have never gotten a tier 6 mission chest. Even after earning two of three platinum medals, completing all optional objectives, and fully exploring the map, we barely scraped our way into the tier 5 chest (based on the progress bar displayed at the end of the mission).

Do certain conditions need to be attained, such as earning all three platinum medals and completing all optional objectives? Are there other "hidden" medals like the Explorer medal, which don't show up until you earn them that would improve our overall score?

Solution 1:

It's all about Total-Score. The earlier the mission (or the earlier in Story-Mode), the harder it is to get a higher Total-Score. So even if you max (All Plat) Utility/Building/Combat + All Bonuses + All Mission Side-Quests (Drone Landing, Storm Chest, ect..) The Total-Score still won't reach the minimum required to pop a Level 5/6 chest. The lower missions simply don't have enough potential score methods. A level 28 Mission can yield a level 5 chest pretty easy if you complete a few side quests, or a Drone Landing (Those things give a LOT of Exp). If you and a well organized team push through a 28 Mission you can get a level 6 chest. If you and a half-organized team jump into a level 40+ mission, level 6 chests are not to bad to snag. Though, will that that said, level 6 Chests just give a bit more of what you're already getting in a level 5/4/3 chest. So if the time it takes you to run ONE mission for a level 6 chest is longer then it would have taken to get two level 4 chests, it's kind of a waste (unless it's a Time-Reward for something you want, then it's worth the extra effort.