Okay, after sometimes I managed to get it working. It was like your second screenshot when I first applied those icons to my start menu. But after I turn off the Rounded corner on menu and menu elements and Restart explorer. The icons look correct now. And I reboot my system and the icons stays as is. Refer screenshot below. Not sure why that option is causing it. I have forwarded your problem to Stardock Support Team for their review. Please keep an eye on this thread for any updates. We appreciate your feedback and patience.
Basj,
Stardock Community Assistant

Thank you,
Basj,
Stardock Community Assistant