Make sure you actually have done some damage to the boss to get your gold. Some dude on reddit (I think) did the number crunching for healers in FATEs so read up on it a bit if you can find it. I stopped getting bronze on boss fates (whilst everyone else in the party gets gold) after I learnt to keep aero up on the boss while healing.

As for Odin/Behemoth there are so many issues wrong with those FATEs that I am not even sure if reward tuning is up there on the top priorities.