Thanks Clay Amerault and Egan Cheung– I thought it might be the case that Engage couldn't "see" the editable sections, as I'm using <tr> and <td> sections with inline styling for text (the <style> tags in the <head> are largely for client-specific styling). This is working for me now after wrapping with additional <p> tags.
Like you say though Egan, what struck me as odd was how moving the <style> tags into the top of the <body> section made the text uneditable, whereas without this code the email behaves normally and could be edited without the need for <p> and <div> tags. It's likely I could be missing something here, but either way thanks both for the advice as it has solved the problem. (for now )
