I've usually measured it with the trap wire on relative spots to the Taipan hull. Although our rig is the same, I don't think these measurements will be comparable.

Anyway, if I tie a string to my trap line and bring it forward to the center of the hull at the bridle attachment point, mark the string, then bring it back to see where it touches the center of the hull--it touches just behind my rear beam. In heavier winds, more rake could be used--glenn ashby told me he raked his T4.9 back to have the string touch the middle of the inspection port lid.