Preview in filter edit mode is so much faster

For some reason, when I open my filter to edit, the final preview image is really quick when tweaking the controls. However, when I exit back to the main screen and tweak the controls there, the filter takes much longer to render a preview.

I have tried creating a small image (100x100 pixels) in standalone and as photoshop plugin, and also tried changing the multi pass and caching options but for some reason I still cant seem to get it to render as quickly as when I'm in edit mode.

Does anybody know why this happens? It's just so much nicer to tweak controls when in edit mode because it's so much faster, and I wish hoping i didn't need to do that every time I wanted to tweak faster as it risks messing up presets etc.

Thanks!