Just some background here:

We don't really have control over this client-side. We are inserting the image at the top of the wikitext (after templates) for all languages, and the backend edit preview response serves it up to us in this order occasionally. I was able to quickly reproduce this ordering on Android as well for Spanish Wikipedia:

The preview endpoint is POST to https://en.wikipedia.org/api/rest_v1/transform/wikitext/to/mobile-html/{title}

Android is going an extra step and inserting the image directly into select infoboxes for EN-only. iOS is not doing this (nice-to-have task). If we're seeing this behavior more often on iOS than Android for EN, that's probably why.