Set the density of trees to 55%. At this setting, there is virtually no chance that the fire will reach the right edge of the forest. Set the density of trees to 70%. At this setting, it is almost certain that the fire will reach the right edge. There is a sharp transition around 59% density. At 59% density, the fire has a 50/50 chance of reaching the right edge. Try setting up and running a BehaviorSpace experiment (see Tools menu) to analyze the percent burned at different tree density levels. Plot the burn-percentage against the density. What kind of curve do you get? Try changing the size of the lattice (max-pxcor and max-pycor in the Model Settings). Does it change the burn behavior of the fire