IMA-SMM3G rules:
6.1.6 Knock-down targets will be calibrated before the event begins.
6.1.6.1 Handgun targets will be calibrated with a 9mm handgun using factory ammunition.
6.1.6.2 Shotgun targets will be calibrated with a 20 gauge shotgun, barrel length not to exceed 26”, using a factory 2½ dram, 7/8 ounce load
of 7½ or 8 birdshot.
6.1.6.3 The Range Master will designate specific supplies of 9mm and 20 gauge ammunition, and one or more handguns and shotguns, to be
used as official calibration tools only by the Range Master or designated testing personnel. Designated calibration firearms and
ammunition are not subject to challenge.
Thus the competitor has to use some common sense - if they choose to run ultra-light loads, they roll the dice on whether their ammo will drop steel. No power factor required.
A well aware of IMGA rules. Actually, a power factor IS required as you state ( I.e. 9mm "factory ammo"). Again, just sayin' it is a bit strange.