I used to be very big on deck armor for capital ships

This is an example of what I used to think was the right way to protect a battlecruiser:

The design had 5in + 4in deck armor, and tapered side armor, tapering from a4in at the top to 8in at the bottom. The belt was backed by 3in armor on the slopes. the anti-torpedo bulkhead, which continued the belt to the bottom, was 2in thick. Between the decks, the funnel protection was 2in, and above the decks was 4in.