On the inhalation the belly presses against the hand and on the exhalation the belly also presses upwards against the hand. While I can generate both conditions I cannot do so without letting the belly relax (drop) between the inhale/exhale. If I end up with my belly extended on the inhale, there's no room for more extension on the exhale. Maybe I'm stating the obvious but is there an implied relaxation of the belly between in/exhale?
Not really. The belly extends in slightly different places on inhalation and exhalation. Don't worry about it. The important thing is that you go really deep in your belly with each breath.
This is "power breathing" with a very strong spirit forward.