Expansion toys: Arrow size should scale

This

a = np.array([0., 0.])
b = np.array([1., 1.])
pt_src = t.PointSources(tctx, b[:,np.newaxis].copy(), np.ones(1))
exp = t.local_expand(pt_src, a, order=3)
fp = FieldPlotter(a, extent=2.5)

t.logplot(fp, exp)
t.draw_schematic(exp)

plt.savefig("out.png")

results in

There should be a way to control and/or auto-scale the arrow width.