Do agree that windscreen interference could be problem. I would suggest lowering it
Meanwhile Tomtom have advised today that they are shortly releasing a new version of the OIS version of the Tomtom Go Navigation app which will have some new features and includes Support for Apple CarPlay. Features include:-
MAPS A LA CARTE:
Customize your map by only downloading what you need with country- or regional-level maps. Select and download just what you need with world wide maps available for download, but in downloadable country or sub regions of ~300-500mb which lets you create your own custom map.
Quick map updates without having to download the entire map again. These small updates (couple mb’s) only replace what is new & delete the data, without needing to completely re-download the map.
MOVING LANE GUIDANCE
Avoid missing turns and last-second merges by zooming in on your lane and seeing all the action up ahead. Allows you to see the road ahead past the exit or junction, again helping to orientate and guide especially when multiple exits occur after another.
The Android version will be available later this year.
Fiat themselves say the holder can hold tablets up to 10 inches, however, they don't say you shouldn't go bigger if you can fit it in, guess, like the comments above, it comes down to whether it obscures your vision or not.