The theoretical immunity zone between Hood and Bismarck

What is the immunity zone discussed for HMS Hood against Bismarck?

It is a theoretical range band where Hood could still damage Bismarck while her own armour should resist Bismarck's fifteen-inch shells.

Hood and Bismarck both carried fifteen-inch guns, so their armour and shell trajectories create a theoretical band of favourable engagement ranges. Within such a zone Hood might retain effective fire while Bismarck's hits should not penetrate protected areas in a decisive way. The idea remains a mathematical model rather than a guarantee. Real shell behaviour, target angle, damage, weather, and fire-control conditions make an actual battle less orderly than the calculation suggests.