You are most likely not doing anything wrong.
What you are most likely observing is the result of two things, intentional design and a potential oversight.

First off the design part.
DRK and WAR have a higher emnity multiplier on their emnity combos.
For DRK this is because they need to use their other two combos heavily to maintain MP for their abilities.
For WAR, they were given a higher multiplier because before they had to rotate through multiple combos to get the equivalent debuff effects that a PLD would get with the RoH combo which was their only 3-hit combo throughout 2.X.
Essentially they were designed with a higher multiplier because they were rotating between multiple combos while PLD only really had their one which was their emnity combo, so it balanced out.

Now the potential oversight. PLD was given two more combos which are not emnity combos and are expected to utilize them to maximize their dps. However, their emnity multiplier was not increased to compensate and so that a PLD cycling through their combos generates noticeably less agro than the other tanks.

Agro generation for tanks has been mentioned as a known issue by the devs and my guess would be that we will be seeing PLD get its emnity multipliers for RoH increased to be more balanced with the other tanks.