The range of any AP is directly related to the effective radiated isotopic power less the attenuation value of any occlusions between the transmitter and receiver. In other words, how much stuff is between you and the AP. In a perfect clear line of sight world, the range could go as high as 600 feet. The 1131 however has a very limited antenna array. When a 100 foot range is mentioned, that is assuming a normal office environment. The 1242 is slightly better due to the use of external antennae. See the attached document that details the diffrence between the APs.
