Questions about the gameplay of Heroes 6.

Hello, I have a question about archers and obstacles, such as city walls or various types of cover on the battlefield. If an archer shoots, how much does the cover or city wall reduce the damage, and how does this interact with the damage if the archer has a 50% damage penalty for shooting at a range greater than 5 cells? And one more question: do archers who shoot magical attacks also have a damage penalty if the enemy is hiding behind a wall or cover on the battlefield, or not?