How to exclude loading from motion analysis?

Good time of the day!
I would like to compare two hulls of similar size but significantly different forms (including different WL areas/KM), and evaluate how forms (only) affects its motions/RAOs. For that I would like to exclude or minimize the effect of loading on motion. So far as loading is out of consideration, I can select VCG arbitrarily (within stability range of course). So if I select equal VCGs (or equal GMTs better?) for both hulls, then results of analysis gives me RAOs, which have changed only due to form and not because of loading. Is this correct? Or are there another method?
Thank you!