11.5 degrees is preferred...
... over 18 degrees. Most racing yachts run 7.5 to 9 degrees for calm water, up to 12 degrees for waves. My Catalina 27 measures 13-14 degrees from the widest point of the toe rail genoa track. Optimum angles vary with boat and sail design. As point of clarification, the lead/sheet angle is measured as a straight line compared to the boat's centerline.... the sail is curved.. so the sail's angle to the centerline at the luff will be much greater than the sheet angle.
An inside track can reduce the lead angle... I would experiment with a barber hauler to check performance changes before I installed a permanent track.