How does covering ally works in Final Fantasy Brave Exvius?

Solution 1:

Quoting the wiki http://exvius.gamepedia.com/Cover

When more than 1 unit are attacked at the same time, the chance to protect party member is based on the order of the party, with left-most unit having the highest chance.

Cover only blocks physical attacks, but if you enhance Golem to have provoke, you could make it more likely for the enemy to attack your tank and can still use cover if needed.

Edit: in case you aren't sure, left-most refers to before you go into battle. That person will be your top left character, but if that's your tank, he's more likely to cover the person below him (second from left).