It's not possible to set the memory voltage, and neither additional tweaks can be tried.
Also, one can't adapt the table to a Vega 56 editor.
Still haven't switched over to xmr yet so I guess I will phrase this as a question. While I haven't played with blockchain drivers in a while I assume its the same as 17.9.x where setting mem volt either in wattman or softtable doesn't change mem voltages but does effectively set a floor for core voltage? This is either a bug in 17.9.x or just how wattman/the card is.
I've always moved mem volts in p3 to at/the same as my undervolt (0.9mv) on the core to ensure it sets effectively.