Surface density (top) and η value (bottom) for discs with α = 0.001, H∕r = 0.05 with an embedded 25 M_E planet. The planet is located at r = 1 and ϕ = −1. A planet with this mass opens a partial gap in the disc density and has reached the pebble-isolation mass (Fig. 1). The η value reaches negative values outside of the planetary orbit over the whole azimuthal range, indicating that taking the azimuthally average η value to compute the pebble-isolation mass is correct.