Editing your preferences wouldn't have changed the unit size set in the traits by the script at the start of the campaign. I'm going to need more information about this guy; I got your screenshots of the prebattle scroll and the victory results, but I need to see a screenshot with all the guy's traits in it.

Here's the relevant portion of code in edct.txt:
Code:
Trigger Imperator_granted_PostBattle_Attacker_normal_UnitSize
    WhenToTest PostBattle

    Condition IsGeneral
          and WonBattle
          and WasAttacker
          and FactionType seleucid
          and Trait UnitSize = 2
          and NumEnemiesInBattle > 500
          and PercentageEnemyKilled > 30
          and Trait BattlePoints > 2
          and Trait Imperator < 1
          and not Trait Bug = 1

    Affects Imperator  1  Chance  100
    Affects Triumphator  1  Chance  100
Possibilities:
1. The UnitSize trait was not set correctly by the script at the start of the game. This can be checked by going into Data\export_descr_character_traits.txt and searching for "Trait UnitSize". Change " Hidden" to "; Hidden" to comment out the hidden attribute of the trait and make it visible. You'll have a new trait displayed, either Small, Normal, Large, or Huge. If this says Large or Huge, it would explain the problem. We'd then need to fix the script, because this affects lots of other things in the mod.

2. The UnitSize trait didn't get passed down the line somehow. Was this guy an adoptee, or did his father die before he came of age? It should still have passed down, but it's possible something isn't working right.

3. You must have fought the right number of enemies (250, 500, 1000, or 1500), depending on the unit size setting. If the UnitSize trait is screwed up for this guy somehow, the easiest fix for you to apply would be to change that "Trait UnitSize = 2" to just "; Trait UnitSize = 2" or delete the line entirely.