Mana Leech is useless

I assume leech resistance is removing the base leech percentage you have instead of lowering it by a percentage. You can have 70% mana leech and leech exactly 0 mana. I built an Acolyte of Chayula with instant mana leech to theory craft a bit and I ended up filling ever gem slot with increased mana leech and have found that any skill that converts any amount of physical to elemental causes mana leech to decrease to between 0% and 10% of the expected leech result based on the damage numbers I see on bosses. I should be able to reach 100% leech by level 90 and do better testing but it's apparent that something is wrong or there is a hidden unexplained mechanic limiting leech to useless levels.

I don't know if it is binary and a skill is either elemental or it's not and it kills mana leech accordingly or something is bugged.

Either way, there should be a way to leech mana and life for elemental attacks. The majority of the attacks in the game including all of the intended primary attacks for Monks are elemental.

Mana is leeched from a % of physical damage, so of course convert physical dmg into elemental dmg reduce the amount of mana leeched.
We should be able to get a leech from any dmg somewhere (tree or armour suffixe) , even with a lower %.
Actually only physical dmg can leech.

The expected mana leech doesn't match the percentages shown in game. I have a physical skill that does 1k dps that leeched more than 10x a skill that converts 60% to lighting despite the converted skill having 25k dps total which means that the physical DPS should be ~10k.

A 10k DPS physical damage skill should leech more than a 1k physical damage skill. It not only doesn't perform that way mana leech is off by a factor over 100x the expected result.