Having looked at the documentation for MediaWiki it appears that there is an option to have the TOC/Index occupy a percentage width of the page
An extenuating circumstance may require the width of a TOC width to be adjusted as a percentage of a page. For example: {{TOC left|width=30%}}
.
I base this on the supposition that most users will use FC on a screen wider than it is deep and that therefore, if TOC/Index can be spread users will not have to scroll down as far to see the beginning of the page content.
Could this be tested in a sandbox version of, say, the manual TOC? If so then we could see how it appears on various screens and what happens to additions and deletions.
While I have done a small amount of editing of the wiki for content, English grammar and readability I am hesitent to make what might be a dramatic change by myself.