​I noticed I was getting ridiculously high amounts of post-battle loot on occasion in my Sherden campaign, so I decided to run a few tests. 

Testing Arena (Screenshot 1): My faction leader, with a fully developed horde, is circled in teal. One of my generals, also with a fully developed horde, is circled in pink. They attack the fort the arrows point at. All tests use autoresolve, and are attacking the same fort on the same turn. In all tests, my faction leader (Metus) initiates combat. 

Test 1 (Screenshot 2): My faction leader attacks alone, with a full horde army (20 units). ​He gets 3613 food etc. 

Test 2 (Screenshot 3): My faction leader recruits a brand new horde and attacks with them reinforcing. ​He gets 4301 food etc. 

Test 3 (Screenshot 4): My faction leader and general, both with fully developed hordes and full armies. They get a whopping 10538 food etc. 

Test 4 (Screenshot 5): My faction leader and general both attack the fort, but this time I disband all the units in the second horde except the general himself. They get 5594 food etc. To clarify, that's [Faction leader with fully developed horde and 20 units] + [General with fully developed horde and only 1 unit]. 

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- From the results, it seems that post-battle loot scales based on the size of the reinforcing friendly army, but also based on the level of horde development. Sea people factions have a building that increases post-battle loot, and the game might be adding the modifiers from all reinforcing armies together. This is probably a bug, simply because the player should not get 10000 food for killing a single general's bodyguard.

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EDIT: Forgot to mention, the save is on Legendary difficulty. You'll have to delete and re=paste the save file if you want to run another test. Sorry about that.

Also accidentally uploaded the wrong screenshot to #5. Fixed.