I've wanted to have a mod like this for my pack, to generate ores in a server-friendly way, but I'm also interested in tiering pretty much everything.
As such, I'm wondering if it would be possible to add another property to the drill-heads JSON, which would increase the amount of ores generated per operation.
The oreResultSize is nifty, but the scenario I'm talking about is: A simple iron drill-head generates 1 ore per operation. I want to have the option to set a steel drill-head to generate 2 ores per operation. Titanium 4 ores per operation etc.

Overall, this would add another incentive for players to use different drill-heads. [This] drill-head might be faster and have more durability, but [that] drill-head will net more ores per vein overall.

Whether or not this drill-head specific gain would be percentage based, additional or multiplicative would be up to you.