The Warfront is kind of a Scenario, where role icons are not available, just test it with default UI and you will see, that even blizzard frames dont have role Icons. So it is not an issue from our site, its more a blizzard thing.
https://www.tukui.org/screenshots/Merathilis/1538753224-voiceoverlay.png Screenshot from the general config of ElvUI. If you dont want double overlays, dont use the ElvUI Voice Overlay. As it stated in the Tooltip: WORK IN PROGRESS! And btw. the Blizzard Voice Chat, is the one over your group frames.