The CSS definition that comes with Theme 25 is based on 12 columns. The definition actually contains multiple fixed grid definitions for different screen sizes. For each definition, the column widths are defined (hard coded) based on the 12 column grid.
Important: the grid attributes in the page template do not define the grid, the CSS does. The attributes/definition in the page template is necessary for APEX to dynamically use the grid definition. The CSS is leading!
If you want to use an 8 column grid, you will have to re-write the CSS grid definition and alter the grid definition in the page template accordingly. So it is possible, but, depending on your level of understanding CSS and @Media queries, maybe not that trivial.
Ahh thanks. I can dabble with CSS but I am no expert.
I was just wondering what effect the Grid Layout and Display Points settings have - was hoping they were for this purpose but I guess not.
I have figured out a workaround now anyway - to generate the contents of the regions dynamically instead of items in region positions.