Why is the volume of wireless handheld Microphone different from that of body pack transmitter?

The volume of wireless handheld Microphone is different from that of body pack transmitter. And either volume of the two is adjusted, the other will be changed as well.  To solve the problem you should check whether the wireless microphone uses mixed output that may lead volume gain adjustment to be imbalanced. Or you could connect two independent balanced output modes, and adjust the volume of each channel through the Mixing Console.