Animator masks ~ Apply an upper body mask to just idle and walk help needed

Hi, So i have this as my base layer for my animator: Picture

When player is doing nothing its in idle when he moves it moves to "IsWalking". What I would like to do is apply an avatar mask that will permanently mask the upper body of idle and walking with: animation refrence

I have the mask setup and understand layers slightly but am not sure how to make sure that the mask applies to just those two animations. The only other parameters on the player is "Die" for when the player dies.

Any help would be appreciated thanks!