I am about to purchase a 2 blade Flexofold for my 99' H376/380. One dealer tells me I need a 17"x15", the manufacture recommends an 18"x14". Says the prop extends 3 to 4" back than a fixed one and can accommate the extra inch due to the angle of the shaft. They also said the extra inch will increase forward punch and reduce prop walk. Any thoughts would be appreciated