On several days in the summer, the height of cloudbase (or the tops of blue thermals) may well exceed 4,000m, but Swiss air law defines certain altitude limits for us to observe. Throughout “MIL ON” times, we are restricted to a ceiling of FL130; during “MIL OFF” this rises to FL150. At standard QNH, these levels equate to 3950m and 4550m ASL.
However, the uncontrolled class G airspace extends like a carpet all over Switzerland from ground level to 600m AGL (with the exception of CTRs, which descend to the ground, and TMAs with lower limits, e.g. for Sion TMA it’s 300m AGL).
Consequently, we may exceed these altitude limits as long as we remain less than 600m directly above terrain, so (for example) even during “MIL ON” we are allowed to fly over the 4274m Finsteraarhorn. However, you would be in breach of air law if you went on a glide from there, and were still over 3950m ASL when the terrain directly underneath you had dropped away further than 600m.