Need help understanding what an "isostatic model minimizing crustal deviatoric stress" means
Isostatic means the equilibrium between the components of the crust in regards to their vertical movement owing to differences in density. 

Deviatoric stress is the kinda sideways stress that particles in a larger system under stress, impose on each other. It's what keeps objects from crumbling to dust when exert vertical stress on them.

So, there model simulates the vertical stress on the crust more than it does the horizontal stresses. Enceladus is a puzzle because it's squished down at the poles much more than any other known moon or planet.