Here is where I am getting my current ideas from regarding the sub-timings...
( dram calculator doesn't have option for Hynix D-die option so this is a stab in the dark. )
( this calc screenshot is not accurate but maybe close enough to get an idea of something to try. )
You could try SOC 1.125v (or 1.05v) but keep in mind in BIOS/UEFI the voltage you enter is not always the voltage you end up with so be very careful as you inch to 1.2v on SOC.
If someone has any Zen2 CPU and this ram kit we might get a good example of something to try if they are kind enough to post their Ryzen Master screenshot of their memory settings.
What was the motherboard again and what BIOS version are you on? This CPU is so new you might reach out to the motherboard vendor for help.