It’s an inherent problem with Physical but it’s arguably better having the projectiles be full sized globs of damage than smaller bits of flat damage that are more likely to be absorbed.
Edit: Actually, since it’s damage converted from Vitality, would it be effected by armour? I vaguely remember someone mentioning recently that Grim Dawn’s coding is made so converted Physical doesn’t adhere to it. Found it: Worst EoR damage.
If Corruptian went from +2 to RE to +3 like @Weyu suggested way up, it’d be possible. Let me go dig an old meme out of my pile.
Using Targo’s helm just for the conversion irks me here because you’re not getting anything else useful out of it - the +1 to mastery bonuses are useless when you want as many as you can get to RE as it’s a naturally unsupported concept and the CDR can be gotten elsewhere. In any attempts I tried putting Physical RE together on a caster, I always went for Ravager’s Dreadgaze instead.