How a first-rate uses its height against a third-rate

How would a first-rate use its upper guns against a third-rate?

It could sweep the exposed deck with anti-personnel fire or keep firing into the hull, with the ships' roll continually changing the angle.

The higher ship could fire across the smaller vessel's upper works to clear men from the deck before a boarding action. Anti-personnel loads could turn the upper guns into very large shotguns. Other guns could continue firing down into the hull. Because both ships rose and fell with the sea, their relative deck heights continually changed rather than presenting a fixed geometric advantage.