Chaos Mastery Leech question

Does the "0.5% of Chaos Damage Leeched as Energy Shield" restore ES based on chaos damage over time or just the initial hit that causes the DoT?

From the wiki it says "Whenever a character with some source of leech hits a monster a leech instance is created."

This makes me think it's just the hit that counts towards the amount of energy shield leeched, and that even if the DoT is much more powerful, it will be ignored for the purpose of leeching. Except that that hit also determines the damage of said instance of leech, so it seems to me that either scenario could be possible if read as written.

I can't actually find any information on the leech mechanic in relation to damage over time.

How does this actually work?

Yep, DoT doesn't leech at all. Only hit damage does. Some other games will allow DoT to leech, but PoE doesn't.