If this is how your percentage is applied then the formula you using is wrong.. A good formula should bring up close to the intended percentage drop rate. If lets look at a claimed 10% drop rate... I do 10 adv it is NOT unrealistic to expect that i should get at least a return on 1 adv... if i do 100 then at least 10 adv must bring a return... I cannot do 30 and get nothing. Then the formula is OBVIOUSLY not working and needs tweaking. Math is math and not luck.. if your drop rate is out of proportion the the formula needs tweaking... simple math...