Denting Blows is not working as intended

The damage appliance of 8.5% is not working as intended, The damage is neglected and lowered on heroes on hit, while on minions it hits completely fine or sometimes go of as intended, but other times it does a 3rd of the normal damage, usually occur on targets with low hp which makes me think that it only does damage based on the hp they have left and not their max hp.

Since its only occurred on targets that have had close to 10% hp left

"Every 3rd attack on the same target deals an additional 4/5.5/7/8.5/10% (+[3500]%) of the target's maximum Health as physical damage, reduces its Armor by 20%"