The drawing is leveled from the design waterline, which is (on the drawing) about 3-4 pixels below the top of the boot topping. The boot topping itself is just an indication of where the ship sits when fully-loaded etc (as I'm sure you know), and since it's just paint, I don't see any reason not to draw it the way it looked in real life.
Allrigth, i was just fooled that the topping was sloped at the bottom part of it, not the top, as it appears to be more usuall