am i using long axe wrong

[Mr. Squeakers]

it says it should activate fortress mode when using heavy attack, but it almost never dose, i thought it might be cause i use a melee attack button instead of equipping the melee each time but holding the button dose a heavy attack and when i test it by equipping melee instead it still dose not activate most of the time.

p.s. i am aware there is a 10 seconds cool down timer and i do take it into account when trying to get it to work,