The CC reduction is increased by the level difference
And elites /champions have bonus CC reduction too.
When you are in inferno your level stays at 60 but the monster reach lvl 63
so they have naturaly CC reduction over you
don t know the numbers but maybe like 10% per lvl difference
so if elites have 50% base CC and lvl 63 => 65 % CC reduction
But the CC work differently with slow stun fear confusion
for the stun the CC reduction will affect duration
but for the slow it will affect the % movement speed reduction
80% slow for 8sec == 65% CC reduc ==> 28% slow 8 sec
4 sec stun == 65% CC reduc ==> 1.4 sec