Xcode Simulator, Chrome mobile view and actual phone showing images differently

I’m testing an app with almost full screen images in ios. The images are 1080x1920 with an approximate letterbox of 165 at the top and 149 at the bottom. The images are set to show full screen. On top I have a row of tabs at the very bottom and a ion nav bar header.

How the images are showing up is changing depending on whether I view it in Xcode Simulator, Chrome mobile view or on an actual phone.

In chrome mobile view phone 6 just a small amount of the letterbox shows top and bottom, in the simulator (target iPhone6) I see about 12px of letterbox gray but only on the top, but on the actual iPhone6 I see no letterbox above or below and actually some of the non letterboxed part of the image on the bottom is not showing (cut off, it;s below the tabs).

How can I get a real ‘read’ from either of chrome mobile view or the simulator? I need to check this on different phone versions, and but only have an actual iphone6 to test on.

Diving me crazy, why are they showing up differently and what’s the best way for a developer work with this / what’s the best strategy for full screen image size that’ll work across all phones when you have tabs and a ion nav bar?