If you look in the Radio tab you can tap on a frequency there to have its coverage briefly highlighted on the map. Also you can long-press to bring up the What's Here menu and select the service.

I'm a regular user of the app when flying, i have encountered issues in flight where the flight information service request i report Sector Boundaries. Unfortunately when planning flights, it doesn't show the sector boundaries in the plan view neither does it show during flight, it would be of great help having this.