I usually replace desktop game launch icons with user-created 256x256 .ico files. I then keep all of the game icons in a folder on the desktop.
Many (but for some reason, not all) of these icons shrink. I have no idea why or under what circumstances. I'll open the folder and many of them have just shrunk. And if I try to replace them, they remain small.
I'm not trying to manually reduce the size. If I scale the icons up to largest size, many of the icons no longer scale up to 256x256 (their native sizes), rather they have shrunk and remain shrunk (to about 96x96) no matter what I do.
I use a piece of software called Free Ico Converter 1.3. It takes jpeg or png images and converts them to .ico. I sometimes have to resize the images in PS first. This is not the first time this has happened. It also happened on my laptop. Just, all of a sudden, out of the blue, some (but not all) of the icons just shrink. I have yet to figure out a commonality between them or a parallel conflict.
I read another place where rebuilding Windows' icon db is supposed to help. I got a batch file that's supposed to do it. I will try it when I get home.