Before revision:  Our model applies if the cell radius, R, is much smaller than the distance , R_{cs} , up to which carrier sensing is effective. The condition R_{cs} >> R is likely to hold in a dense deployment of Access Points (APs) where, for every client or station (STA), there is an AP very close to the STA such that the STA can associate with the AP at a high Physical (PHY) rate.
After revision:  Our model applies if the cell radius, R, is much smaller than the distance , R_{cs} . We argue that, the condition R_{cs} >> R is likely to hold in a dense deployment of Access Points (APs) where, for every client or station (STA), there is an AP very close to the STA such that the STA can associate with the AP at a high Physical (PHY) rate.