In many transport and reaction processes of interest in chemical engineering, rapid velocity variations are known to take place near porous media boundaries. However, modeling the extension of the resulting boundary layers has been the subject of a long debate in the literature. In specific, modeling of momentum transport between a porous medium and a fluid has suggested the inclusion of additional terms to Darcy's law. The origin of such corrections may be regarded as a result of an upscaling method used to derive the governing equation at the Darcy scale. To address this issue, in this work we perform pore-scale simulations in an idealized porous medium model consisting in arrays of straight channels that allow obtaining analytical expressions for the Darcy-scale velocity profiles by performing an averaging (instead of an upscaling) operation. Our results show the dependence of the size and shape of transition layers with the size of the averaging domain when studying momentum transport between a porous medium and a fluid but also near the porous medium-wall boundary. With this low-computationally demanding methodology, we can conclude that the existence of an average velocity boundary layer, and thus the pertinence of correction terms to Darcy's law, is certainly justified.