Endurance charges - elemental reduce damage and convertation

On the Juggernaut (+1% physical and elemental damage per endurance charge) 15 endurance charges + legacy (no limit on endurance charges charges in 0) Eternal Damnation amulet with chaos resistance 70 // also did 20 endurance charges - the effect on elemental damage is similar (I describe the situation below).

RF without regen and with minus fire resistance does not deal damage.
It would seem that this is immunity to elemental damage?

Next, we convert 100% physical damage into elemental/chaos damage with Chaos Inoculation (tested with the Watcher Eye for 22% conversion, Lighting Coil for 50%, a rare helmet for 8%, or 2 copies of Innsbury's Blade for 10%x2=20%, or a DawnBreaker shield for 20% - tested both options)

Attention to the question of game mechanics:
Why does damage pass from white mobs from normal attacks without penetration?)

I would also like to know if penetration elemental damage works to reduce damage from endurance charges: according to my tests on Atiziri/Uber Atziri, it does not.

In my humble opinion, this is a clear "logical hole" in the game mechanics.