Ignorance is bliss
With the B&R rig the power is achieved from the main sail. In this case the main has most of the sail area and the jib is small.On "conventional" rigs with a backstay the power is achieved from the Genoa and a correspondingly small main. In this case the designers sail plan takes into account the center of effort for BOTH sails. That is slightly forward of the boats center of lateral resistance.Sailing with a B&R rig is a little different and you will eventually learn how to trim the sails to achieve the best pointing conditions. The designers sail plan has taken this into account. I know I read the sail plan provided by Hunter.By adding a larger Genoa the fore sail center of effort is moved further aft. Moving the boats overall center of effort closer to the center of lateral resistance (usually the center of the keel). On close haul points (where we really like to sail) the center of effort moves naturally aft and off center since the boat is healed over and the hull is no longer symmetrical in the water. With a larger fore sail, on rigs not designed for them, the weather helm will be greater on closer points and reducing weather helm will be harder.The only advantage to adding a larger fore sail will be in light winds on a reach or run. But that is what spinnakers are for.