Cumulative Rosseland mean opacities in discs at 1 AU with different α viscosity parameters and for different fragmentation velocities. The main contribution to the opacities is from the small particles below 10–100 μm or when converted into Stokes numbers from particles with Stokes numbers of less than 10⁻⁴, where particles are perfectly coupled to the gas and are thus not blocked in the pressure bump generated by the planet.