Could you elaborate ? Did you have any particular parameter in mind.
To me the model seemed strikingly simple with just 6 parameters. All assumptions seemed very mild, benign and sensible. Furthermore they list out the behavior and the nature of the equilibrium at different settings of those parameters.
There could be different points of criticism of the work, but over-dependence or sensitivity to finely tuned parameters does not seem to be very strong to me in this particular case.