Treesaver doesn't currently support variable column-widths within an article -- this is due to performance reasons (supporting variable column widths would make layout much, much slower).
To clarify, you must have a consistent column width per article per device. This means that a "Sports" article can have a different column width than "Entertainment" article. Or an article can have a different column width on the iPhone than on a desktop -- but you can't mix within the same article.
If you want to have different sets of grids for "Entertainment" and "Sports" -- you do so by setting the data-grids attribute on the <article> tag:
<article data-grids="sports">
That will restrict Treesaver to looking only at Grids that have class=sports.
- filipe