I have the following setup and it works:
iPad Mini 2 (Wi-Fi only) tether to my iPhone6 via Bluetooth, and the iPad Mini 2 connected to the Solo controller via Wi-Fi.
I also have an extra Bluetooth device - Garmin GLO for actuate GPS used in the Solo app.
Before flying, connect the iPad mini to the local Wi-Fi and open the Solo app, view the satellite maps on the home screen for your flying area (zoom in and out), then re-connect Wi-Fi to the Solo link. Connect the iPhone via the Bluetooth connection and check internet connection using Google maps or Safari. Make sure that your iPhone Wi-Fi is switched off.
Start the pre flight start-up with Solo and check the in-flight maps before flying, the Bluetooth tether connection is very slow, so it takes a few minutes for the in-flight maps to refresh, be patient.
The Garmin GLO is great of all the functions that required GPS position of the controller - Follow Me, "Return To me" etc....
The GPS from the iPhone is not very accurate, and the Garmin GLO works: GPS + GLONASS.
From my experience, it took a few sessions to get all the systems working, so I would get everything working while the drone is on the ground, trying different connects and configuration while flying is not advised.
Be safe and happy landings..................