Patrolling planes vs Planes attacking the patrolling planes

My intercepters were patrolling, and I found enemy’s tactical bombers were trying to attack my patrolling planes.

Before combat,

The enemy’s: 4 of 1 level tactical bombers. The health was 41.0/80

Mine: 3 of level 1 intercepters and 2 of level 2 intercepters. The health was 74.7/97

After combat,

The enemy’s: The health point became 31.6/80

Mine: The health point became 72.1/97

The enemy’s planes got damaged only about 10 points even though my planes had over 20 defense damage. And mine got 2.6 points of damage. Considering 1 level tactical bomber has only 1.2 attack damage against planes and their health was about half, that was their full damage against planes.

Therefore, planes attacking patrolling planes attack with their full damage, but the patrolling planes defend with their half damage. It’s not fair. Patrolling planes should defend with their full damage when they are attacked.