Since units get attributes improvement, they are more valuable in battle and tougher to defeat, let players get an adeguate loot.
Comparing an elite unit with a champion unit, their stats are very similar.
here the proposed loot comparison:
Elite Swordman: 15food 10 wood 15 metal 100 xp
Champion Swordman: 10 food 10 wood 15 metal 150 xp
Notice that swordman has +5 metal of loot by itself, it means that any other unit wiill have:
15 food + 15 wood + 10 metal in case of archer / pikeman /spearman at rank 3
15 food + 10 wood + 15 stone in case of slingers at rank 3.
I'd suggest to increase the champions food loot by 5.