Even when I use push-to-talk, my voice doesn't seem to activate as if the sensitivity was too low. If I yell, it picks the signal.
Someone theorized that the game uses a non-configurable voice activation level even when using push-to-talk. Some people were able to fix this by increasing the mic level in the Windows audio settings.
I however can't do this as I use an USB microphone with its own specific driver. Windows mic settings don't work with it and I can't boost the signal.