Left: contours of the binary envelope penalty function in θ,φ, with the largest plus symbol indicating the minimal value, and the other symbols indicating the next two best values. The best solutions are seen to exist in two degenerate islands. Right: the remaining free parameters α_c and v_max as a function of the penalty. The two islands of solutions give similar values for both parameters, so the choice of solution does not affect the physical interpretation of the event, beyond the direction.