I'm pretty sure it depends on whether you have Zoomed mode enabled (which effectively renders everything at iPhone 6-size then enlarged) or Standard, which just displays more 'stuff'. Probably depends on your Dynamic Type settings too.
I have mine on Standard and Dynamic Type on one from the smallest so it ends up just showing a lot more than the 6, however I've seen people who use Zoomed mode with very large Dynamic Type, which is great if you have visual problems.