The slot cover only fits that one case, or at least only Inwin cases. I've been building PCs for more than 30 years and I have never seen a PCI slot cover that is bend the over way around - thus nobody would every expect that it exist. There should be a disclaimer in the shop at the product level, that it ONLY fits to the Inwin s-frame case.
You also didn't get my issue, it's not about the dimensions, the bend is the wrong way around, this is not a slight modification. I wish I could show a picture - but the linking feature doesn't work for me.