Looking more into the plans, I found 2 other things that I don't have answers for:
1) did Bismarck have extra magazine protection ?
From the plans, I can see the vertical protection consists of the 320mm main belt + 120mm inclined portion of panzer deck + armored bulkhead (45mm below the scarp, 30mm above it). The horizontal protection appears to be 100mm Wh.
My question : did the walls of the main magazines have extra armor ? Some splinter armor perhaps ?
2) How were the funnell uptakes protected from damage ?
As far as I can see, above the panzer deck there are 5 x 2 uptakes that transfer smoke from the boiler rooms to the funnell above. They were located in the sections XI, XII and XIII, spanning about 30m in length, 15 in width and some 5 meters in height.
Now, those uptakes had only citadel protection (145mm KC n/A + 30mm transverse Wh bulkhead).
This is not enough to stop heavy gunfire.
In the event of a battle, a single shell explosion exactly in the center of the funnel uptakes would destroy them all, leaving the boiler rooms unable to evacuate smoke (in fact, they could evacuate it, but it would be inside the ship)
This would almost certainly lead to drastic speed reduction and death.
What am I missing ?