Why is the volume on Cortana so low when on Bluetooth?

[Windows Central Question]

Cortana volume on blutooth low

Lumia 1520, windows 8.1 on developer, The problem is have is the volume of Cortana when connected to blutooth. When the phone is not connected to blutooth the volume is fine but when connected to the car the volume is about 13 out of 30, when you ask a question or get a text you cannot hear her unless you whack the car volume up to 30 to hear it, when the call ends and it goes back to radio / cd mode, the volume after setting to 30 blasts your earlobes out as that is now the volume of music, you quickly have to turn volume down by audio controls of steering or by the radio.
I have previously tested putting the blutooth volume at level 25 when its connected to car and you get the pop up, volume this high may cause damage to hearing. I'm not bothered about that as long as I can hear cortana via blutooth. Then after you turn phone off overnight and turn on in the morning. The blutooth volume resets.

My question is, is there any way to keep the volume of blutooth or Cortana above 20 without it resetting every time you turn it off then on. I had the exact same problem before putting dev preview back on my new mobile at the weekend