Note that Bismarck’s bow was modified from a straight stem to the ‘Atlantik’ bow after launch, while Tirpitz’s bow was modified before launch.

This has made me think (perhaps incorrectly) that the underwater portion of Bismarck’s bow was never modified (because that would require drydocking) and that the above water portion of the new bow was curved into the old below water straight stem. However, since Tirpitz was modified while still on the slipway, her bow could be modified both above and below the waterline, leading to less curvature.

But I have no proof of this.