Getting ~1% damage reduction on pet from Whistle of the Beast?

Good evening,

I purchased Whistle of the Beast for soloing fun, which says it increases pet armor by 10%, and when my pet is sitting around ~6k armor (including 1k from beast training), the whistle only gives it around 300, to increase damage reduction by about ~1%. Is this working as intended? Is it only taking from some base armor value of around 3k?