Could it possible to shrink thy L-ground polygon a little bit? (the question is to the BT module designers)
I will consult with the Module Design team, but I know (and you know too) what they will tell you.
Broadcom provides example layout guidelines to maintain optimum RF efficiency for our embedded module RF characteristics.
Any deviation from these sample layouts may not provide the desired performance.
Modeling deviations from the layouts provided will change the performance, as you are aware.
RF design is a mathematical layout "art form" and although many techniques are implemented and copied, many are not successful because of reducing the Keep Out areas on the layout.
We engineers want to "cheat" RF Design with reducing size of Ground Planes and it usually never works.
That being said, since the embedded antenna in our module reduces the board floor plan that would normally be taken up by a Chip or PIFA antenna, you already have the best of both worlds - smaller PCB and NO real estate needed for an external antenna!
I will consult with the Module BT Team and relay your request.
Hope this helps.
Modifying the ground plane and speculation on the associated tradeoffs are discussed in this thread: Re: BCM20732 layout options
It seems that other users have made changes to our recommendations and accepted the associated tradeoffs.