@F-Berbenni
You are right. As example, here is the 0°C isotherm altitude above the highest summits in the Alps shown by ICON-D2. And ECMWF with a coarser resolution displays quite the same map in Windy.
DEB35BA8-955A-493B-ADA8-6D75509A844D.jpeg
Freezing altitude (0°C altitude) at 3000m level seems inconsistent. At same location Airgram by same model displays the 0°C level at 850hPa (1500m asl approx.)
Another app shows a similar map by the same model. So it is due to the way how this model compute the iso-0°C.
D3A6A983-43E9-490E-9CFF-7CB4C6080B46.jpeg.