Read through this post;
https://forum.45homelab.com/t/pcie-cards-are-not-sitting-flush/778
It won’t solve your issue directly, but they do seem to have QC issues with the PCIe area spacing on some cases. You can try moving the back of the case as described in one of the comments. I’d email info@45homelab.com and let them know you are in the group of buyers with these issues. Obviously removing the brackets from the cards is not acceptable.