For once we disagree Simon. I think an armful to be the max, but very soon you will want to begin easing just 10-20cm before sheeting in again. It is all about feel for the boat and the conditions. Anyway, key is to not accidentally adjust rudder angle while sheeting the main.

I dont know how much the mast moves while sheeting the main going downwind and how that changes the spi shape. Never been in a position to study that.