Differential gamma-ray flux at 50 TeV, either measured from LHAASO-KM2A source sample (blue dots) or extrapolated from the H.G.P.S. catalogue (red dots), as discussed in the text, as a function of the minimum zenith of observation from the northern sites (left panel) and the southern sites (right panel). Differential sensitivity lines of IACTs are also shown for comparison at different exposures and for extended source observations, as indicated in the legend.