Hi @Ant_Forshaw,
TinyMCE strips out most tags that wouldn’t be used as part of the options that are part of TinyMCE. You can see an explanation of this here: Adding images to announcements in OJS 3.3 - Tiny MCE - #4 by rcgillis
Did you try the config.inc.php option that you used with the announcements: Announcement Images with custom size not being scaled on frontend- TinyMCE - #4 by Ant_Forshaw
-Roger
PKP Team