Hey Randan,
pretty much every 42mm I’ve ever tried/seen will fit in the Stooshie. Some 45mm tyres might fit but I don’t know which ones will and which ones won’t which is why we suggest 42 is the biggest. Two other points :
1) The standard TRP fork on the Stooshie is the limiting factor on tyre width, not the frame (the Lauf fork in that picture has more clearance than the TRP).
2) Frame size affects clearance, bigger frames have more clearance than smaller (although the smallest frame still have 35mm with mudguards and 42mm without as minimum).