I know that formations, vegetation, yell, relief etc. affect the troops, but how exactly?

- A testudo protect you against arrows. But how? Does it increases the defense? What about wedge, phalanx?
- I looked the files up because of Egyptian fighting in snow etc. there is just one number for each reagion. Does this number affect the moral? Attack damage? Or what?
- Does the yelling increase the damage? How exactly?
- If a unit has to climb a hill they have disadvantages fighting units at the top. Which one?
- Do higher ranks increases the moral too or attack and defense only?