The only crystal property that affects the effectiveness of a PrismLens is Purity. Size does not increase the number of PrismLenses crafted, unlike Lenses.
Astral Tome entry
While crystal lenses are useful, sometimes it is desirable to direct the light onto multiple locations simultaneously.
After some testing, you have concluded that having a crystal acting as a prism and splitting the outgoing Starlight evenly across the facets would be most effective. It would function like a Crystal Lens, but evenly split outgoing Starlight to all target locations.