Differential flux of LHAASO first catalogue sources as a function of their radius, measured (circles) or upper limits (triangles), as evaluated by (a) WCDA at 3 TeV and (b) KM2A at 50 TeV. The colour code refers to culmination at zenith angles below 30° at each observatory sites (red for CTA-South, blue for CTA-North and ASTRI). Filled markers in the right panel correspond to UHE sources in LHAASO first source catalogue (with test statistics at 100 TeV TS₁₀₀ > 20). Lines show the ASTRI and CTA differential sensitivities as a function of the source extension; dashed for shorter observation time and solid for the longer one, as indicated in the legend that applies to both panels.