unless I'm applying something wrong here, if 150 power = 8% damage, then (700/150) * 8 = 37.
someone with more familiarity can correct me, if I am wrong.
You have to take scaling into account as well.
Damage increase with strength is not a linear curve.
The more strength you have, the smaller the bonus will be.
Formula for Damage: Damage = Weapon strength * Power * Skill coefficient / Armor
Since weaponstrength, Skill coefficient and armor are the same, we can exclude these,
so we just have to calculate the percentual difference between Power without EA, and power with EA.
Assuming base power of 1000: (1150-1000)/1150 = 13.04%
Assuming base power of 2000: (2150-2000)/2150 = 6.98%
Assuming base power of 2500: (2650-2500)/2650 = 5.66%
Assuming base power of 3000: (3150-3000)/3150 = 4.76%
Ofcourse, Empower allies also affects allies, so the total damage increase will always be higher in group