A% Function with calculated key figure

I am getting incorrect Percentage value on calculated KF.  In my query I have a total for calculated KF for current year and previous year.

               KF A      -      KF B      =      Calculated KF

2011      5,000      -     1,000      =          4,000

2012      6,000      -        500      =          5,500

Formula 2012 CalcKF A% 2011 CalcKF = 170%   (6000 / 5000 = 120%) + (500/1000 = 50%) = 170%

I would like the result to be 5,500 / 4,000 = 137%      How can I achieve this result?