Filemaker have not yet updated FMGO to take advantage of the iPhone 6's extra screen size.
While the screen resolution is mentioned in the stencil sizes, the application is unable to render or scale them appropriately on either the 6 or 6 plus.
In the interim if you need to get going with some layouts, your best option is to scale everything to the iPhone 5's screen size for it to display correctly on the 6. Hopefully an update is not far away. I share your frustration on this, buying a new device with extra resolution and screen size and not be able to use it as intended is becoming annoying at this stage.
Wow, thanks for the reply. Nice to know this information. I appreciate you taking the time.
Thanks for the post above, I sincerely appreciate it.
FMGO app update 11/20/2014 thru App Store has fixed this issue!