There is absolutely NO need for the complication of find a the "LP" of a genoa to determine the percentages you want for the foot dimensions for a roll-up to 135 or 100%, etc. LP is a simple direct ratio of foot length.

A genoa for this sized boat will NOT have roach of any significant measure ... its not a symmetrical spinnaker its a genoa. The 'roach', or as a sailmaker would call it an apron, will only extend several 'inches' and therefore will only add less than 1% of the foot length (as a tangent ratio).

Just measure the exiting foot length and ratio that value by what you want .... (X)135/155 or (X)100/155 and youll be within 1±% of the 'actual' or 'spherical' dimension.

... and the rest of the world wonders why the USA is in 40th place out of ~195 countries in Math education .....