In two earlier articles (Tappin, Eyles and Davies in Solar Phys. 290 , 2143, 2015 , and Solar Phys. 292 , 28, 2017 ), we used the stellar photometry to determine the calibration parameters and long-term trends of the Heliospheric Imagers (HI) on board the Solar Terrestrial Relations Observatory (STEREO). In this article we provide an update on these determinations for the ahead spacecraft (STEREO-A) to incorporate the interval after solar superior conjunction (when STEREO-B was non-operational). We describe the modifications needed to our photometry procedures to accommodate the reduced pointing stability following the switch-off of the spacecraft gyros shortly prior to conjunction. We find a small revision to the absolute levels is required. We also show that the very low rates of degradation (less than 0.2% per year) found in the earlier determinations have continued beyond solar conjunction.