Hi Jules,
I do that too. But I now use the extra large Print view screen and hold the CTRL key as I select a few images  I want to resize.
Then I double click the blank space either below or to the right of the print view and pop into the Page Editor to be able to place them exactly where I want them on my page.
 
Mike even set it up so you can see the event just before you resize.
See screen snap and notice cursor pointer. It advises you how many you selected and that you will be resizing those images.

Stay happy,
Fred

The live view on the main window is where you do your general sizing, borders, etc. and you can multi-select as many prints as you like on that view.  The full page editor ("Edit Page" button), is intentionally single select because in the page editor you are fine tuning individual prints and many of the operations there don't make sense with multiple prints selected: crop adjustment, location fine tuning, etc.

So on the main window in the center live view of the page, multi-select as many prints as you like with shift/ctrl or even right click and "Select All".  Then on the Prints tab, choose a size like 5x7, 8x10, etc. and all selected prints become the size you click.

Regards,
Mike