I vaguely remember this topic. It was just after Beronath, Reforged got 100% Elemental->Physical conversion (hence a lot of Physical conversion builds started becoming popular). What’s odd though was I remember them testing PRM converted to Physical damage which if what is known now is true means it shouldn’t have been effected by armour at all back then.
Testing armour for a modder shouldn’t be hard though as it’ll just be about creating unique enemies with certain stat characteristics for different scenarios and recording numbers. For example, DenisMashutikov did the same a couple months back to showcase that the old RR formula was incorrect.