The notion that fatbikes can ride on top of deep snow is false. Fatbikes still need a compressed based on ride on, the level of compaction needed to keep from sinking is much less than a normal bike, but there are limits. Under certain conditions (moisture content of snow), up to a certain depth you can compact the snow on the fly, but it takes a huge amount of effort to keep plowing forward. The snow I typically encounter is very dry and doesn't pack, so it doesn't need to be too deep to make me bog down.