Mike, I'm not sure you cited the correct paragraph? QW-403.6 is what deals wth range of thickness for impact testing and even then only addresses minimum thicknesses. Impact test requirements are ALWAY a function of the constructing code, not the qualifying code.
However, for reference, here's what QW-403.6 says: QW-403.6 The minimum base metal thickness qualified is the thickness of the test coupon T or 5⁄8 in. (16 mm), whichever is less. However, where T is less than 1⁄4 in.(6 mm), the minimum thickness qualified is 1⁄2T. This limitation does not apply when a WPS is qualified with a PWHT above the upper transformation temperature or when an austenitic material is solution annealed after welding.
In my edition of the ASME IX Code, your reference to QW-409.22 reads as follows: QW-409.22 An increase of more than 10% in the amperage used in application for the first layer.
In this case, QW-409.22 is for hardfacing and corrosion resistant overlays.
Are you, by chance working with temper bead applications?