rig tuning question

[charrette]

i recently installed a backstay adjuster on my fractional rigged hunter 35. the rig has aftswept spreaders with uppers, intermediates and lowers. the forestay is tensioned mostly by the upper shrouds. in order to maintain the proper pre-bend (2") that matches my mainsail the backstay is set quite loose (5%) with the uppers at 24% the intermediates at 16% and the lowers at 10%. when the backstay is tensioned to 20% of the breaking strength i get the desired bend (7"-8") to flatten the sail. when the backstay is tensioned the uppers are at 20% the intermediates are at 15% and the lowers are at 12%. i am concerned that the backstay is too slack when set for the pre-bend. any insight would be appreciated.
thanks.