Have you tried going to say
Harken.com and gone thru the online program that will customize a set up for you? IIRC it will also tell you how much pull in pounds you will get from a given main sail, depending upon boom length, Sq footage etc. It allows you to play with it some.
For you, with where you have it, moving it forward some to behind the cabin as I have, Tenuki etc, may make it so you do not have a knee kicker if you will. a bit more forward, where a 6-1 setup would more than make up for increased pressure if you have a 4-1 currently.
Not sure where to find the program online that you speak of, but I am sure it exists to some degree, it may be the
harken compuspec, or something else, but you do not see it working as you would like per say.
marty