@ Golden Rivet, Gysbrecht
I don't think CCF will explain it.
the CCF is [1+(V/g)*dV/dh]^-1
If I apply that at 140 kIAS @ T=0 and T=30 I get:
CCF = 0.9824 and 0.9801 respectively (H check my sums?)
That's only 0.2% difference but the gradients differ by 5.79/6.03 = 4%