Just my two cents worth...fully agree with what Ted just said.
Fooling with FMs, and considering them right, is a real toss-up.
Realisticly (especially for CFS3 FMs), to make one 'correct', it needs to be run through one of the right workbooks. CFS3 FMs have many of the newer entries in 'em, so, if you try to adjust something in an airfile, there is a good chance there is another entry that also needs that adjustment. That won't happen, unless the airfile gets worked correctly. There are literally too many 'unknowns' in the airfiles.
I've gotten racked for saying this before, but what the hell. For any FM, they have what I call hard numbers...and soft numbers. Hard numbers??
That's what I call any measuring number, weights, dimensions, control surface movements, climb rate, etc.
Soft numbers are any other entries, such as prop settings, lift, drag. Each of those you adjust to get the right performance, etc.
To me, those 'hard' numbers need to be right first, or it's just a waste of time. That's the starting point.
A good example is a new P-47D-25 FM I've worked on. NO names, but once I put in my 'hard' numbers, which I fully researched, I compared with two other FMs for the same airplane.
Just a simple matter, but one FM had all the control surfaces dimensions too big, the other too small. Yup, double-checked all numbers. Any idea how much just those particular numbers affect the accuracy of a FM?
My point, if the hard numbers are wrong, what else is wrong. Alot of FMs also have interpetation needed for many entries. Interpetations that need to be at least somewhat realistic.
Lol! Okay...three cents worth.