Jet opening angle, θ_j, for the three fiducial ideal MHD solutions. The weakly relativistic XRBId solution displays weak collimation asymptotically, as evidenced by the decrease of its opening angle with z, while the AGNId and GRBId solutions feature near-radial or freely expanding streamlines. At low z, the opening angles of all three solutions increase, as the jets are decollimated by the positive transfield component of the Lorentz force.