Cannot turn off autosize column widths on a matrix

Looking at some of the posts and ideas it appears there is no way to create a matrix, in the new version of the matrix visualisation, and fix the column widths?

I have a matrix and even with the autosize columns widths switched off I cannot manually determine the column widths of the matrix. The column widths always snap back the length of the largest value in the matrix.

I can see the use in this but it's not that useful when you want the matrix to be a fixed size on a report. I can't see what the auto-size column width toggle actually does?