Helpful info:

1. To resolve positioning issues with full screen Reveal modal popups on iOS using Foundation - add data-v-offset="0" to the modal like this:

    div class="full reveal reveal-modal" id="site-reveal-menu" data-reveal data-overlay="false" data-v-offset="0"
      div class="page-content"
        ...

Read about: foundation/foundation-sites#9763 (comment)