Think of it this way: Filters like this, USM, HPF, etc. all have a "length scale" or "radius" (in pixels) that you can set. If you set the length scale to, say, 10 pixels, it's effects will spread out over 10% of the width of a 100 pixel wide thumbnail. In contrast, the effects of the filter will spread out to only 0.2% (ie, 10/5000) of the width of a high resolution, 5000 pixel wide image. The first case will likely be too dramatic of an effect, whereas in the latter case, the effects will hardly be visible.
To confuse matters, a few filters, notably, some 3rd party plugins, are aware of the above problem, and instead of letting the user set the length scale in pixels, they adjust the length scale in percent of the size of the image. In these (fairly rare) cases, you would see almost no difference in the effect (other than the expected pixelation) as you change from small to large images.
HTH,
Tom
!
