Displaying Box Model in Visual Aids seems a bit random

I find the Visual Aids very useful but I've always found it difficult to get the Box Model ( \\\ and ///) to show. I've since found you need to put the cursor in the element's containing div tag, but it also works when cursor is in an img tag as in the first example.  In these two examples all visual Aids are on, both have the cursor in the img tag but only the first image shows the \\\  The button in the first image correctly shows the surrounding \\\.  The house image in the second page has CSS of img {padding: 20px; margin: 5px 5px 5px 400px;} but the \\\ does not show. Has anyone found which circumstances will always show the \\\ and the ///  ? Both are in Design View in DW 2017.0.1

first page is at http://v26.ancestry.higgsy.co.uk/backmaster_letitia.php

second page is at http://v26.ancestry.higgsy.co.uk/one_element.html