I have the Landy main too and the technique seems to get the pre-bend into the ballpark setting. On the older boat I fitted Tornado adjustable spreaders as I wanted to have a play with settings. On the newer boat I have the standard fixed length and angle spreaders - I'm considering changing them to some I can adjust for angle.

John_P now supplies shorter carbon spreaders with notched positions to allow for different rake angle. I may well retro-fit a set to my newer mast......