Loss Diagram Calculations

I have another questions regarding the loss report. I am trying to make sense of how the math works, and I cannot seem to follow the method. For example: I have a nominal DC energy value of 18,187,460kWh, and a net DC energy of 15,859,220kWh. The ratio net/nominal is approximately .872, or a .128 reduction in energy produced. The problem is that summing the individual losses results in a loss factor of .13134.

The total loss is not the sum of the percentages. For example, from the default Detailed Photovoltaic / Residential case:

Nominal DC energy (kWh) = 9,029
Net DC energy (kWh) = 7,847

The Net/Nominal ratio is 7,847 / 9,029 = 0.87

The individual losses reported on the loss diagram are:

Module = 9.049%
Module mismatch = 1.973%
Diodes and connections = 0.493%
DC wiring = 1.973%

The total loss is then (1-0.09049)*(1-0.01973)*(1-0.00493)*(1-0.01973) = 0.87

Best regards,
Paul.