Air loss into porous media effect on velocity

Hello all,

I am trying to model air up a small hole (10 m long but very narrow). On one side of the hole there is a porous media which should cause air to be lost from hole into the media. I would expect that this would cause a dip in air velocity once reaching the porous media area but instead I see an increase in air velocity. If there is mass loss into the porous matrix this shouldnt happen. I am not sure how to define the outside edge of the porous media (furthest from the hole) to allow for air loss. Any help would be appreciated.

Attached is the model.

Thanks!