Garmin 340 Audio Panel Split Com

Does anyone out there have experience with Garmin's 340 audio panel and
its feature that lets you split the Com 1 and Com 2 so that the pilot
can talk/receive on one while the co-pilot can talk and receive on a
separate frequency on another? It is called the "Com 1/2" button.
On my installation, the co-pilot experienced that Com 2 reception was
blocked with I was talking on Com 1. That is not how it is supposed to
work. I have been told by one avionics shop that it is difficult to not
have Com1/Com2 interference and that I should just write-off this
feature. Another shop said that the Com 1 and Com 2 antenna's had to be
relocated so that they were on opposite sides of the plane (one op top
and one on bottom). I am not sure what to believe at this point. Any
advice or experience that folks have had would be appreciated.

-Sami
N2057M Piper Turbo Arrow III