Closure triangle formed by Chilean stations (ALMA/APEX), LMT, and SMT in 2017 (left panel) and 2018 (right panel). The LMT-SMT baseline is the shortest baseline between non-co-located stations in EHT observations of 2017 and 2018. Black markers: observed closure phases. Red line: fit to the DoG-HIT reconstruction in 2017 (left panel) and 2018 (right panel). Dark blue line: fit to the DoG-HIT reconstruction (ring) with an additional Gaussian model component determined from 2021 data as it would appear in 2017 (left panel) and 2018 (right panel). The line has been offset by a time offset of 0.1 hours to make it visible. In the bottom panels, we show the significance of the difference between the DoG-HIT model and the DoG-HIT model with additional Gaussian component, measured by the difference in Ψ_C divided by the closure phase error. In both years, the effect of the additional Gaussian component on the Chile-LMT-SMT closure phases is an order of magnitude smaller than the respective noise.