The hurtbox for the ore isn't a cube exactly, but it is made of fairly large cubes (think Minecraft) so it can easily be attached to the terrain even when the visuals say it isn't. The situation you're trying to arrange is for the ground surface to not intersect with even one tiny corner of those invisible cubes, either by digging it below or raising it above.

https://valheim.thunderstore.io/package/JereKuusela/Ore_Support