Location of the different outcomes of radial migration in the (p,q) plane. Dashed (resp. dotted) line: limit between accretion without or with grains pile-up resulting in a finite or infinite time in the A-mode of the Epstein regime (resp. B-mode of the Stokes regime at small Reynolds numbers). Shaded area: location of observed discs. Black dots: discs used as examples in Sect. 3.3.