Not parent; your comment made me think, is that?:

- swipe down from anywhere in the vague middle of the page?

- swipe down on the right hand edge where an "invisble until you need it" scrollbar might be lurking?

- swipe down at the "not quite the top/bottom edge of the screen" because you don't want the OS swipe, you want the app swipe.

Aarrrgh! I don't even have an iPhone and the options drive me crazy.