acs71020 Connecting and reading voltage properly
If you get 150mV amplitude (300mVpp) with 230VRMS and the maximum voltage measured by the part is 275mV amplitude then your full scale voltage is actually 230VRMS * (275mV/150mV) = 421.66V. This seems like normal design to me, providing some margin for safety as well as providing a range of measurement values for inputs above and below the 230V nominal.

Does using 421.66 as the full scale voltage give you a reasonable answer?