How did full plate armour affect the size of knights' shields?

As plate armour became more sophisticated and provided enhanced, comprehensive coverage for the knight, the need for a large, kite-shaped shield diminished. Consequently, the shield evolved into a much smaller implement.1

This trend aligns with a broader historical principle in military technology: generally, the more effective the protection afforded by body armour, the smaller the shield required by the soldier. As plate armour replaced chain mail and offered a rigid, glancing surface that protected the wearer from head to toe, the knight could rely less on a large shield for defense and more on the mobility and coverage provided by the suit itself.213