That adjustment tool is to change the size of icons, (and icon previews) in finder windows, but has no effect on the size of images, other than the icons for those image files.If I understand your question correctly, all you have to do (when you're in icon view) is adjust the slider at the lower right corner of the screen.
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If I understand your question correctly, all you have to do (when you're in icon view) is adjust the slider at the lower right corner of the screen.