Gap depth as a function of planet mass for different disc viscosities at r = 3 AU and 10 AU. Grey bands mark the range of values for f_gap that can be generated by zonal flows (Flock et al. 2015). Black dots mark the pebble isolation masses as computed from Bitsch et al. (2018). For α ≤ 3 × 10⁻⁴, the pebble isolation masses are in the deep gap regime while higher α results in pebble isolation masses within the shallow gap regime.