Tilt evolution over time, i(t), in terms of binary orbital periods. Runs: r1 (solid blue), r2 (dashed blue), r3 (solid red), r4 (dashed red), r5 (dotted red), and r6 (dotted blue). For comparison with r3, we also plot the symmetric curve of r1 with respect to i  =   90° (solid green). r3 shows an anomalous behaviour because the disc breaks in two discs after ~ 150 orbits, which then evolve towards polar alignment (see Sect. 3.3).