Ok, nevermind. This is no longer necessary
I found this post that shows how to unhide a section of the bios to uncover the “aperture size” setting:
As I was following it and applying the same to my BIOS, something didn’t quite match because it appeared that aperture size for my BIOS was already visible…there was no “IF statement” to hide it.
Yet in the BIOS it wasn’t there.
It turned out that the entry has been unlocked by Gigabyte in one of the latest firmware updates and all I add to do was to clear the CMOS and it now shows correctly in the BIOS. (It still isn’t mentioned in the manual).
Thank you for you help.