-atk +res innes

It is not fixed, it is simply used.

+res is good for ploys. If you use def ploy, you have virtually gained more atk than you "lost" through the bane. (In fact, you never had it; you simply got Innes with 30 atk.) You can also stack spd ploy on it; you will hit the fastest units in the game including Nino+10 using fury unless she has a res boon, in which case she only has 43 spd and you'll compete much more easily. If you use fury, you'll probably ploy even the dragons. Some will hit 34 res but usually not 37 without a breath skill or close/distant def which don't count when ploys get applied.

If you're using the effect refine, you might like special spiral + iceberg. Squishy mages die to the iceberg on Innes' first counterattack. Any dragon you double gets hit with the iceberg.

If you don't have special spiral, QR2 can be an inexpensive option for dealing with hyperspeed mages. As long as you can avoid their double, you win. (And I've never seen a fast mage using bowbreaker.)