The druids of orboros officer's * attack The Devouring, states this:

Lets say we have a full unit, so 7 models in the unit.The Devouring (★Attack) - The Devouring is a RNG 10, AOE 4, POW 8 magic attack. Add one to the POW of the attack for each model in this unit.

Ok on models directly hit its pretty obvious that the pow will be 15.

However on the models suffering blast damage its 1/2 POW. So I assumed it would be pow 15/2 = 8 (rounding up).

However I stumbled across the rules for how to handle modifiers to 'stats'. And it appears you should first half the base stat (8) then add the +7 for a pow of (half of 8 plus 7) 11 on blast damage.

So which is it? In other words is the 'base POW' of the attack 8 or is it the 15 when a full unit is present?