From ErfWiki

Proposed Canon

A combat bonus (also referred to as force multiplier)^Erf-b1-p125 is a positive circumstantial influence that increases unit stats and makes it more efficient in combat.

Bonuses can derive from^Erf-b1-p125:

• Leadership
• Terrain
• Stack (maxes at 8 units)
• Artifacts
• Special abilities
• Spell buffs
• Dance-fighting

Bonuses are very important in the combat system of Erfworld. In order to win a side should increase bonuses for their units while decreasing bonuses to enemy units.

Speculation

Assuming that Wanda is level 8 and Ansom is level 10, then Summer update 33, the bonus seem to be.

Leadership bonus:

Chief Warlord

Global: Level/3

Same Hex: Level/2

Same Stack: Level

Chief Caster (if matched to caster)

Global: Level/8

Same Hex: Level/2

Same Stack: Level