Wither and despair not applying to monsters with Poison ranger gas arrow chaos damage

Have been using Poison ranger with despair and wither on hit (raging spirits dumpster fire from fire wall) just to attempt to apply negative chaos resistance and I'm now certain it just doesn't apply at all. Did two boss runs today and both had the same reasonably same TTK with and without chaos resistance debuff. Despair I use can go to -47% resist and wither on hit from raging spirits brings the total up to 90-105%~.