the /EFI/BOOT subdirectory is a common standard: https://members.uefi.org/specs/esp_registry
I have not retrieved the UEFI specification wich details its usage, but there is a Fedora doc that explains it a little the shim (SecureBoot) case. And I seem to recall that years ago, I needed to manually copy /boot/efi/EFI/debian/grubx64.efi to /boot/efi/EFI/Boot/bootx64.efi for Debian to boot.
