The hardware reference manual http://ftp1.digi.com/support/documentation/90002181_K.pdf refers to a keep-out area
below and above the module of 0.150" ( Page 68)
Getting the CCIMX28 closer to the your board will not affect performance of the CCIMX28. The distance was set to make sure we never have a clearance issue. We guarantee that if you maintain the keep out they will not have a clearance issue with the part if something needs to be changed in the future (there are no changes scheduled at this time, but…).