The mechanical engineer who designed our heating / cooling system placed the CO2 sensors for the gymnasium (with bleachers) in the return ducts. He has indicated that ASHRAE 62.1-2007 defines the breathing zone as 3"-72" above the finished floor; he argued that the return grilles for the space were located 12"-58" above finished floor, where the CO2 detectors are located inside the duct. Since all the air is being returned from the breathing zone and the air is being measured for CO2 prior to mixing with any other air stream he contends this should comply (as the system will be running when the space is occupied). The reviewer did not agree and indicated the sensors were not installed in within the vertical constraints of the breathing zones of the performance gymnasium space as defined in ASHRAE 62.1-2007 and as required by this credit. Has anyone successfully attempted this strategy for CO2 detection in a LEED project? Thanks!