Like-with-like assortment plus exponential fitness increases cooperation, even under weak selection

arXiv “Assortment and the evolution of cooperation in a Moran process with exponential fitness”

I am still struggling to understand when it would be appropriate to assume an exponential (rather than linear) fitness function. It is wonderful that these modelers are mapping out all these different conditions under which cooperation evolves, but how to select an applicable model for real-world applications remains elusive.