I'm not sure if it will stick up that much despite the height difference. Chances are your torso is not 5 inches less, more than likely an inch or two.
Anyway to answer your question, the top of the frame and bottom of the frame are essentially in encasements. There is a gap between them that allows this flexibility, however there needs to be some play in between them for torso adjustments etc. The minimum, they could probably be would be 20 or 21 inches just due to how pieces fit together and needing a little space between the encasements and to allow extensions to fit on etc. Now you can probably get the frame to not extend beyond your shoulders, but it would require the hipbelt being dropped a bit so it doesn't fit directly over the illiacs. If you are not trying to obtain shoulder lift then the hipbelt is really only for stability anyway so dropping it a bit isn't much of an issue. It does still support a load even when it is a little low, just not as well.
