I don't see any references to the information you're throwing out, please link a specifice reputable site.
Also, Parson isn't that much bigger than most of Stanley's units. Hobgobwins and twolls are only a head shorter than Parson, and the uncroaked are about 2/3 Parson's size. It's not likely that siege weapons will be based the stature of the ruler, who happens to be smaller than a large portion of his main fighting force.