Delayed the top-unit load 300ms and viewability jumped

Delayed the top-unit load 300ms and viewability jumped
Tried this nerdy one — the above-fold unit was loading before the hero image, so it rendered, scrolled out as the image pushed it, and logged a non-viewable impression.
— Delayed top ad call ~300ms until layout settled
— Stopped counting impressions on units that scrolled off
— Viewable rate 61% → 79%, RPM on it +14%
An impression that never gets seen still dilutes your viewable rate and your CPM. Make them count. Test it on one page first.