From the pic (if I picked out the correct boat) your jib luff curve is not quite matched to you mainsail curve .... I would try moving your jib leads back slightly and if at 13knts of wind you are backwinding the mainsail, move the jib traveler out alittle to open the slot ... You are close through

Sail Flat, Sail Fast, Sail Safe
Harry Murphey
TheMightyHobie18/#9458, Fleet54/Div11
P19mx/#86, CRAC