In 2016 I posted this:
"Adjustments can be made for small changes in the filament current. The risk is that the regulator chip may overheat if too much current is drawn, especially if the power line voltage is also high. We have not determined how far you can deviate from the standard 1.2 amps without risking failure of the chip, so the risk is yours."
The design incorporates some margins for power line voltage and ambient temperature variations to ensure reliability, but there is no design margin for more than 1.2 amps.