Windows Folder Preview Icons

I've recently changed the default icon for my folders, but folders containing files still show the folder preview icon, with the file pictures as part of the icon. I was wondering where these images are generated from, so that I might modify them or disable them.

Also, top priority is to not interfere with the image thumbnail previews, because they are tremendously helpful.

Thank you for any information you can provide about this topic, even if it might not present me with a simple solution.

Here is a picture of a folder with the new icon I'm using, alongside a standard folder preview icon.



If I could have every folder look like the one on the left, It'd look much cleaner to me. I used regedit to change the icon, but couldn't find information on changing the folder preview icons.