Hello,
I just took another look at the construction plan.
The wall in which the niche is integrated has a thickness of 23 cm. Electrical and wastewater pipes also run through this wall - furthermore, our house is a timber frame house, so I can’t provide you with the usual masonry wall thicknesses.
I was also mistaken - the niche starts above the 5th tile row, not as I previously wrote above the 4th - according to the plan, the sill height of the niche is 1.38m.
However, our tiles are not, as I previously claimed, 30 x 60, but 25 x 70... - then the sill height including joints and sealing also fits...
Regards,
Dirk