Questions about how experience is gained
 

Do you get experience for killing enemy units that are summoned? Such as units summoned by a Friendly Gremlin. So if the Gremlin summons more enemies during battle do you get more XP for that battle than if you killed just what the battle started with? Also enemy thorns summoned by Royal and by each other, Demonologist, Druid, Dryad, etc.

Also, do you get more experience from a battle if you have fewer stacks of units. Meaning if I enter a battle with just 1 stack of Black Dragons and win do I get more XP than if I entered with the full set of 5 stacks?

Also does the power of your army ratio to the power of enemy army affect XP at all? Meaning if I've got a really weak army but defeat a powerful force do i get more, as opposed to if I've got a massive army and kill off just a few bears.

Does anyone know of any variable factors that affect the XP gained from battles?

I don't know for whether you get it for summons. I do know none of the other stuff in your post affects it.

You do get for summons. You get 0.017 XP per point of leadership, regardless of the stack, and regardless of your army composition. This is why I'm doing a test playthrough with max Black Knights to see if bosses can be exploited this way :)

As for the XP gained for battle, this is what modifies it:

Learning - up to 20%
Hand of Necropolis (gloves) - 10%, game can spawn 2 of them
Memoirs of the Marshal (artifact) - 5%
Shark Tooth (regalia) - 5%
Chain of Chance (belt, with gift bag) - 5%
Treasure Searcher medal - 7%

so in essence, you can get up to +62% XP per battle.

Are you sure about this? So in a suppression battle I could keep a friendly gremlin alive, pound away at the summoned enemies, and get more XP for this?

If so, this would be something to consider when suppressing items, especially level 4-5 ones.

I will have more data on that soon. I'm almost done with the playthrough where I'll leave a boss to summon more and more units and see whether they count. However, they should, because looking at the formulas and game files, it says 0.017 per point of leadership. There is no mention of stacks, summoned units and such.

Logically, that should include the summoned creatures as well.

Understood. I'm not sure if they changed it in KBAP, but in KBTL I'm pretty sure summoned units don't count towards XP. This is because in KBTL I've done multiple suppression battles on the Elven Crown (used it while killing elves at Ellinia) and while the gold varied, the XP is always the same.

But do continue with your analysis, they might have changed the XP formula in KBAP.

Hmmm, a mighty, mighty fail. I read a post were a guy said he finished the fight against the spider at turn 90 and got 77k XP for it on normal, so I assumed that summoned creatures count.

Well, they don't. Just fought the spider, summoned stacks went over 10k units (!!!), but the Black Knights' stood tall and managed to kill them. This is the first time I saw the Attack value go over 1000 (frenzy for the win!), but that was all there was to the fight. The end result was 11k XP with Ancient Knowledge scroll on. There is no way in hell this battle can provide 77k XP in one go.

EDIT: Oh, well... This can only be utilized for posterity. Damage inflicted in this battle went up to 3.5 mil. Now that was carnage.

One last comment to the original poster:
While the comparison of your own army to the enemy army does not affect XP gained for your hero, it DOES affect XP gained for your pet dragon.

KD

Am I to understand that extending a fight to allow for more killing of summoned creatures does NOT give Amelie more xp, but WILL give the pet dragon more xp?

Well, not really. Usually extending a fight means leaving the enemy with a single small stack. Therefore the ratio of the enemy's current leadership over Amelie's current leadership will be very close to zero. And that's how much extra XP the dragon will get with each skill used at that point... almost zero.

KD