Gigabyte Z390 Aorus Pro : ultra fast boot not working ?

It seems that the "ultra fast boot" setting does not work on the Z390 Aorus Pro : it is not faster than the "fast boot" option : the POST stage requires about 10 s in both cases which is quite long. In the bios, I disabled everything I don't use and disabled CSM and secure boot. I installed Windows 10 in UEFI mode and the EFI system partition is on the Windows disk too.

Is it a bug ? On Asrock motherboards, ultra fast boot is faster than fast boot and enables to have a POST time of less than 5 s.

Win10 boot/shut took way longer when I compared it with win8. Ultra fast boot,CSM or secure boot didn't help.
Asrock/Msi optimize their boards better though.