Dynaudio Problem?

I would very much appreciate it if EOS owners with Dynaudio would try something for me:

Listen to a CD at a decently loud volume and then fully fade the sound to the rear. What do you get?

When doing this in our EOS the sound all but disappears in comparison to when faded to the mid-way point, ie evenly distributed between front and back speakers.

I sat in the back earlier today with my missus driving. With the top down you can barely hear the system and with the top up it all comes from the front with the system having to be turned up very loud to be able to hear it at a half decent volume in the back.

I would be very grateful if you could let me know if this is normal behaviour as I have the car booked in on Tuesday so could mention it to the dealer then.

Thanks in advance for your help.