in the surf world, australia we call it from the back, so a 3 ft wave has about a 6-8 ft face.
however, in the USA they call it from the front, eg, when they have the big wave events, and they are on a 20ft wave, they are measuring from the front. Therefore our 3ft wave to us is a 6ft wave to them.
But like I said in oz, look at the front and half it, otherwise you will sound like a goose!
I think with windsurfing, if you are talking about the wave you are on, same as surfing, you can safely refer to it as "head high" (3 ft wave from rear), "mast high" ( 5ft wave from rear).
Thats my understanding anyways, from pretty good sources I should add!