So the CL in CDi is CL = CLa * (AoA + AoA_0). (Where AoA_0 is the AoA @ CL=0)
Have I understood you correctly?
This equation also returns differences between the real FSX CDi and the calculated CDi. When the difference in CDi vs altitude is plotted on a chart, the chart gives a regular curve that is almost linear. This leads me to assume that something besides parasite drag and induced drag is causing this difference. With jets such as the B738, the difference between calculated Net drag and measured net drag isn't significant. However, with planes such as the B744, the difference is rather noticable.
Note that the tests were carried out in ISA conditions and with unlimited fuel, where the fuel level is 0. I measured the values after the plane had been completely stabilized in terms of N1, FF and Net thrust. Also, the calculated air file table values were correctly linearly interpolated.
Note that I've tried the following:
CL = CLa * AoA
CL = CLa * (AoA - AoA_0)
CL = CLa * (AoA + AoA_0)
CL = CLa@CL=0 * (AoA)
CL = CLa@CL=0 * (AoA + AoA_0)
CL = CLa@CL=0 * (AoA - AoA_0)
Since there is one exact way that FSX make planes behave, the presence of variations either means that the equation isn't complete/correct or that something has been miscalculated along the way. I've spent a great deal of time making sure that there are no mathematical errors, which means that the equations that I use aren't complete or correct.