Bluetooth headsets are Class 3 - less than 10 meters in clear space. But if the phone is on the other side of your head from the phone, the range is about 2-3 feet - your head absorbs most of the signal. (I keep my phone on my belt, on my right side, but my right ear is about gone, so I have to use a Bluetooth headset in my left ear. It doesn't work well unless I take the phone out of the holster and put it into my shirt pocket [left side]. But if the phone is on my desk and I go out for the mail, almost 30 feet, I can still use it - as long as my left side is toward the house.)
That's just the way it works, so you have to have the phone on the same side of your head as the headset is. Your body absorbs too much of the signal if it has to go through you to get to the headset.