recent changes on development reference sim and mod directly in runDEoptim, but these are not passed to the function (and documented). passing the entire (large) simList is a problem because it may contain non-serializable objects that can't be passed to a cluster.
since it's only the following objects that are being used, we can pass them individually to the function instead:
sim$fireSense_spreadFormula
mod$thresh
P(sim)$lower