Something about Shattering Palms

I've noticed when my hero has one hundred skill points in Shattering Palms skill, he was never able to land critical hits on heroes and special characters ( i know that heroes are immune to death blows ( or at least shattering palms ), but i'm talking about normal critical strikes triggered by combat difference )

Here are the 1v1's i've had:

Empire Monk ( me ) vs Knight Healer
    65 Combat        vs 42 Combat
  0 Critical Strikes   vs 3 Critical Strikes

Empire Monk ( me ) vs Empire Hero
   70 Combat         vs 51 Combat ( even 29 when stunned )
  0 Critical Strikes   vs 4 Critical Strikes ( 3 or 4 not entirely sure )

High Elf Monk ( me ) vs Barbarian Warrior ( Level 54 ) *** My monk here has Elden Prowess
   65 Combat          vs 55 Combat
   0 Critical Strikes   vs 0 Critical Strikes

Minotaur Monk ( me ) Vs Orc Shaman   *** My Monk has 100 skill points in ferocity
   206 Combat          Vs 68 Combat
   0 Critical Strikes    Vs 2 Critical Strikes

2 fights worthy of mentioning :

 - When i removed the points from the skill ( 0 shattering palms )
I've ran a test against an Empire hero , ( my 98 combat vs his 58 combat) , i was able to crit naturally, and did around 3 almost in a row

 - I tried a high elf Monk with 100 points in Shattering Palms, and around 78 points in Weapon master ( 100% chance ) , and indeed, i was able to crit 100% of time