How Germany might have answered plunging fire after the Falklands

How could Germany have improved battlecruiser protection after seeing the danger of plunging fire at the Falklands?

Later designs could have used a much thicker armoured deck and a turtleback-like protection scheme, although completed ships offered little room for change.

The question starts from the problem revealed by the Battle of the Falkland Islands: existing ships could not simply be redesigned after completion. Later German battlecruisers might instead have adopted a heavier protective deck. A turtleback or Elswick-style approach offers one possible solution. Combat evidence could therefore influence the next design generation even when the current ships remained fixed.