I finally figured out how to edit the layout of the User Profile page (Luna template) from the default cbPosLeft: 49% / cbPosRight: 49% layout.
You can either edit the CSS file directly: components/com_comprofiler/plugin/templates/luna/template.css
Note - the header remarks in the Luna template.css contain the following warning - /* Name: Luna. DO NOT MODIFY: also used for backend. */ ...so treat this hack with caution!
Original template.css:
Line 97 .cbPosLeft, .cbPosGrid { float: left; text-align: left; }
Line 99 .cbPosRight { float: right; text-align: right; }
Note - the default width for both of these two elements is 49%.
Edited template.css:
Line 97 .cbPosLeft, .cbPosGrid { float: left; text-align: left; width: 25% !important; }
Line 99 .cbPosRight { float: right; text-align: right; width: 75% !important; }
Note - if you don't include "!important" then your new width settings will be overwritten by other css elsewhere - I nearly went crazy until I discovered this trick!
**OR** as I later discovered...!... just go to your CB Comfiguration Manager - User Profile tab and set the '2 colums layout widths:' to 'Left: 25% Right: the rest!'
The learning curve can be a tough climb sometimes!