Increase the threshold from 62.5 cm to 75 cm

But a flatter roof does not increase the eaves height?

No, but the [Drempel]

Would fully utilize the eaves height and if you don't have a ridge height, just make the roof steep... then you will already reach a reasonably decent height with only 10 cm wall distance (e.g. 10 cm at 45°, 14 cm at 55°, or just a mansard roof - if something like that is possible)

Eaves height does not matter, maximum eaves height 4m and maximum 45°! The room height on the ground floor is 2.64m plus ceiling and we need to be a few cm above the top edge of the drain. I don't know if a wider roof overhang can still make a difference...

Just go to the building authority and ask if there is a tolerated exceeding or possibly other roof shapes that might be permissible.