I believe originally, long leaders even above 15ft in length were used, but I have never bothered and neither have I seen such lengths used.
My leader length is normally less than 3ft (1 metre) but attached to a polyleader of 10ft (of various sinking rates). If I'm not using a polyleader (e.g. summer and tiny flies) I use 10 to 12ft.
Hope this helps
Colin
Ps. Underhand casting is rarely talked about now. It sort has become incorporated into modern spey casting techniques.
