My theory is that 100 Potency isn't an *1 Modifier. It's closer to 1.005, or 1.005/100 = 0.01005 per point of Potency.

10 = 0.1005
20 = 0.201
30 = 0.3015
40 = 0.402
50 = 0.5025
60 = 0.603
70 = 0.7035
80 = 0.804
90 = 0.9045
100 = 1.005
150 = 1.5075
200 = 2.01