After looking through the config i cant find the HQ Metal stacksize option.
The HQ.Metal.ore is there but not the metal its self
HQ metal No option for higher stack size
Better look again , you must have missed it. its in the DATA config
{
"ItemId": 317398316,
"Shortname": "metal.refined",
"HasDurability": false,
"VanillaStackSize": 100,
"CustomStackSize": 600000