Mortarion is 30 feet tall

According to plague war, the emperor made him twice the size of an average human, so he was fairly tall for a primarch.

But the gifts of nurgle made him 30 feet tall. According to Google the average giraffe is 18+ feet tall. Mortarion is the size of a telephone pole?

Seems like guy haley may be playing fast and loose with that as how could he be taller than angron?