Wayne, you've got PM.

Some more on fluting in armour from Peter Krenn and Walter Karcheski’s “Imperial Austria, Treasures of Art, Arms & Armour from the State of Styria” (1998). The fluting/corrogation added strength to the armour without adding weight. This was common in Maximillian (Austrian) armour which blended German Gothic and Italian styles. I suggest it also added Ottoman features as fluted helmets were common there, some suggest to resemble folds on turbans.

Fluted armour indeed adds rigidity and blunt force impact resistance. It's like using corrugated iron roofing as opposed to flat sheet metal. Makes little difference to penetration by sharp and/or fast moving projectiles, unless the valleys in the fluting are designed to guide any projectiles into glancing off. It's the hardness and thickness that counts then.