The parameter is only used in the TSMFK01 model.
The "k_AB" parameter is only for very slow forward exchange rate.
The extected values should according to the reference paper:
Tollinger, M., Skrynnikov, N. R., Mulder, F. A. A., Forman-Kay, J. D., and Kay, L. E. (2001). Slow dynamics in folded and unfolded states of an sh3 domain. J. Am. Chem. Soc., 123(46), 11341-11352. (10.1021/ja011300z)
The paper conserns values of k_AB in the region 0.1 to 5.0.
If the exchange rate is any higher value of this, then another model should be used for the analysis.
