Panel a: comparing the torque from the disc between a − δr and a + δr (solid lines) on m₁ = 5 M_⊕ planet (red lines) and m₂ = 3 M_⊕ (blue lines). The lighter colours represent the torques from the simulations with a single planet and the darker ones for the co-orbital simulation. The same colour dotted lines mark the torque from the whole disc. The y-axis is the scaled torque and x-axis the distance from the planets’ orbit in unit of their mutual Hill radius R_H. Panel b: perturbed surface density. Two horizontal lines are drawn at 1 and 5R_H from the planets’ orbits to guide the eye. Panel c: torque on m₂ as a function of distance from the planet. Panel a is the cumulative torque but this panel and panel d show the torque only from the grid cells at a given distance from the planet. The dashed and solid lines belongs to the outer and inner disc, respectively. The colour code is the same as in panel a. To ease the comparison, we plot the negative of the torque from the outer disc. The symbols mark where the torque on the planets change due to the presence of the second planet. Panel d: same as panel c but for m₁.