Amplification damage should not count to the triggering damage.

Code:
[01:10.73] Treant Protector receives Living Armor buff from Treant Protector.
[01:12.19] Treant Protector receives Plague Aura debuff from Undying.
[01:14.03] Undying  hits Treant Protector  for 47 damage (2126->2079).
[01:15.13] Undying  hits Treant Protector  for 53 damage (2097->2044).
[01:16.19] Undying  hits Treant Protector  for 50 damage (2061->2011).
[01:17.26] Undying  hits Treant Protector  for 48 damage (2028->1980).
[01:18.33] Undying  hits Treant Protector  for 46 damage (1997->1951).
[01:19.39] Undying  hits Treant Protector  for 52 damage (1968->1916).
[01:20.46] Treant Protector loses Living Armor buff.
[01:20.46] Undying  hits Treant Protector  for 46 damage (1933->1887).
[01:21.53] Undying  hits Treant Protector  for 130 damage (1890->1760).