HGPS (H.E.S.S. Collaboration 2018) source fluxes (markers) as a function of their extensions at (a) 10 TeV and (b) 50 TeV, compared to the differential sensitivities (lines) of ASTRI and CTA for different exposures. Sensitivities are evaluated at a zenith of 20° for ASTRI, whereas in the case of CTA we span different zenith angles up to 60° with a band. In the right panel, source fluxes are extrapolated up to 50 TeV by assuming a power-law or/and exponential cutoff power-law spectrum, according to the indication of the HGPS catalogue. Sources marked with a grey cross in the left panel are unidentified ones, while a plus marker to the right indicates sources without any detected cut-off by H.E.S.S. The colour code indicates the culmination zenith angle of sources at the ASTRI location, corresponding approximately to that of CTA-N. Note that low-zenith angle observations with CTA-N correspond to high-zenith angle observations with CTA-S. The LHAASO-KM2A differential sensitivity is also reported.