I am noticing a few interesting things perusing the battle logs.
1. The leader bonuses cancel each other out. If a 3-2-2 general attacks a 3-1-1, the attacker's units will gain 5%*(2-1), or 5%, to their to-hit chance.
2. Leader bonuses cannot to-hit below normal. When the 3-1-1 fires back at the 3-2-2, the formula again is 5%*(1-2), which would be -5%. However, it cannot be below 0%, so the actual bonus is 0.
3. Final to-hit cannot be below 7%, even in an element with no cohesion.
4. Sharpshooter are actually quite inaccurate (although you can already tell this from the unit card)