Was looking for an article to explain a bit where and why the Dexcom has the range it does..
Part of it has to do with Dex wanting its sensors not to interfere but at the same time stay small..
(even though the articles a bit old, it still applies)
http://medicalconnectivity.com/2006/03/03/fcc-deals-with-mics-vendors-help-and-hinder/
This article explains about the MITS band (where pacemakers, other CGMs (Medtronic) and such lie and how Medtronic doesn't think Dexcom belongs in this frequency band, but yet their CGM does.. Even though another pacemaker manufacturer (Biotronik) actually sided with Dexcom saying there shouldnt be a problem with their device)