Just a testing zone.
Leech Page Test:
All leech mechanics act the same way for life or mana. Examples in this article will use Life, but if the character has equal statistics for mana, mana leech will behave identically.
Whenever a character hits an enemy while having an applicable source of leech, a leech instance is created on that character. Each leech instance is independent, and will heal the character for Damage Dealt #% damage leeched as life at a default rate of 2% of that character's maximum health per second. Thus, each leech instance will have a different duration, calculated as (HealAmount / (MaximumHealthPool * 0.02) ). Each leech instance will stack and apply to the character simultaneously until it expires or the character is at full life. However, if the total leech per second from all leech instances is greater than the character's leech cap, the extra healing will be ignored. By default, this cap is 20% of their maximum life pool. This means that a default character only receives life from up to 10 leech instances at the same time. The life from any additional instances is lost for as long as the character has over 10 leech instances.
Leech can be modified significantly through passives, support gems, and equipment. Beyond just adding various sources of leech, modifiers such as #% of maximum Life per second to maximum Life Leech rate or #% increased (or reduced) Life Leeched per second can change how leech is applied to a character.
The #% increased (or reduced) Life Leeched per second modifier provides an increase to how much life per second a character will regain from each leech instance, without changing the duration of the leech instance. This will increase the total amount healed by that leech instance. If previously a leech instance would heal your character for 100 health over 1 second, and you gain 20% increased life leeched per second, it will now heal your character for 120 health over 1 second.
The #% of maximum Life per second to maximum Life Leech rate modifier provides an increase to the amount of life a character can leech simultaneously. A character with 10,000 life can only leech health at a maximum rate of 2,000 per second (10000 * 0.20 = 2000) regardless of how many leech instances they have and what rate they individually regain life. If that character gains 5% of maximum Life per second to maximum Life Leech rate, such as from the notable Vitality Void, they will be able to leech up to 2,500 life per second. (10000 * (0.20 + 0.05) = 2500)