Gareth, thanks for your reply. This is an interesting issue, and as I looked into it, I couldn't verify that it has anything to do with Collapsed Topics, so it is probably not in your jurisdiction. But here's the problem.
I have added some custom CSS to MORE in order to get the center display to be full width. The code looks like this below (yep, a lot of these fixes.) However, I am finding that some of this code reacts differently when in edit mode, or when not in edit mode. I will attach another screenshot showing this. Maybe Mary will have some insight.
Here's my CSS code to try to force full width:
/* Move main content left. Note: This will erase any blocks to the left.
This might be eventually fixed with MDL-47156 */
#page-grade-report-grader-index #region-main,
#page-admin-setting-themesettingmore #region-main,
#page-course-edit #region-main,
#page-grade-edit-tree-index #region-main,
#page-enrol-instances #region-main,
#page-grade-report-singleview-index #region-main,
#page-admin-user #region-main,
#page-question-edit #region-main,
#page-question-import #region-main,
#page-admin-report-log-index #region-main,
#page-user-editadvanced #region-main,
#page-admin-setting-appearance #region-main,
#page-admin-roles-define #region-main,
#page-grade-report-history-index #region-main,
#page-report-progress-index #region-main,
#page-admin-setting-debugging #region-main,
#page-mod-quiz-report #region-main,
#page-grade-edit-letter-index #region-main,
#page-report-outline-user #region-main,
#page-question-type-description #region-main,
#page-backup-restore #region-main,
#page-enrol-unenroluser #region-main,
#page-enrol-users #region-main,
#page-backup-backupfilesedit #region-main,
#page-course-management #region-main,
#page-backup-restorefile #region-main,
#page-mod-forum-discuss #region-main,
#page-mod-forum-view #region-main,
#page-mod-assign-view #region-main,
#page-mod-forum-post #region-main,
#page-user-forum #region-main,
#page-mod-forum-search #region-main,
#page-report-log-index #region-main,
#page-grade-report-user-index #region-main
{
width: 100%;
}