BackGroundDetect cant detect low level audio

Hi to all;
I m working on BackGroundDetect.If callee has hard phone it can detect any voice comes from callee side.But if callee has mobile phone,it can not detect voice unless callee puts his mouth right on the microphone (which looks really awkward).Is there a way to decrease threshold value for detection?

Thanks in advance

AMD(Answering Machine Detect) is much more sensitive than BackGroundDetect.In addition to this it can decide whether human has answered or machine has answered and it has a conf named amd.conf which includes settings for detection.