Totally agree with you on all this - why would you use such a small section of screen? Can you expand on what you did to get this full screen with WAZE on IOS? Are you doing screen mirroring?
I can't speak of how it works on Android, but with IOS it's easy. The Waze integration is native to Sync 3.3 and 3.4 (our version) might also work natively with earlier 3.x versions but can't confirm that.
Anyway, in IOS case you disable CarPlay for the device and then plug it in with USB, it won't work over Bluetooth on IOS. Fire up Waze on your device and Applink will jump in and show Waze as a Mobile App ready to be used. Again.. if you try to do this through CarPlay you will have Waze jammed up in the upper 1/3 limited by the confines of that upper section and CarPlay.
Given the limitation of CarPlay in the upper 1/3 I have completely disabled it. I feel it's useless now, which really stinks as I feel the phone integration, Spotify, Maps etc. etc. are much better with CarPlay. Worked great in my 2018 F150.
The bummer is as a Spotify user, without CarPlay we no longer will have the tight integration with the ability to find music, rate songs (thumb up/down etc.). For whatever reason Spotify stopped supporting the integration with Applink (Ford's Sync integration application) in early 2018. So without CarPlay... spotify use is crippled.
Interestingly enough... Pandora integration works not only on USB but ALSO on bluetooth. I have to have Pandora open on my phone and it will show up in Mobile Apps without needing to be plugged in. So I can have my iPhone on the wireless charger and still get full Pandora functionality... thumbs ratings, browsing personal content etc. So clearly the Bluetooth integration of these applications is possible... since Pandora is doing it. Would be great if Waze, Spotify and others could work like this.