There was a very impressive production of Agamenon at Stratford years ago (late 70's) where the cothurni were close to a six inch lift and the mask with a headpiece or ankus extended height close to a foot. There were arm extensions as well. This gave the appearance of the actors being like statues close to eight feet in height; certainly larger than life. Those ancient theatres were quite large and this helped those seated in the last rows.