After reading this and the other test you did, i feel forced to change how i think claims work.
In the good 'ol days, two miners could find the same claim, and it was the first person to get there that claimed it. This led me to believe claims were 'in' the ground before hand. Then the mining system changed and you found the claim instantly. I had always assumed that MA changed the entire system and removed claims 'in' the ground. But after all your tests, the more likely scenario is that they never changed the 'back end system' and only changed the front end and that claims are still 'in' the ground waiting to be found.
So here is my, mostly, unproveable theory.
1) Claims are spawned in the ground.
2) The amount/type is decided after the avatar finds it - which would take into account finder/amp of the tool used.
3) Claims are 2d, there is no depth calculated before the claim is found.
I guess from a programming side of things, this is also probably the easiest. And also would go with the double bombing tests done before. The likely hood of a second claim was consistently low and, in my view, in line with a random distribution of claims 'in' the ground.
Rgds
Ace
EDIT: there is one thing to consider. Someone years ago managed to land on an asteroid in space, and managed to mine and actually found a lyst claim. Why would MA have claims in space at all? This for me is (small) evidence that claims are generated at the time of drop, but not enough to convince of my thoughts from above. Something to ponder.
Also, MA dropped a purposeful 150k mining claim during an event, for publicity - not 100% sure it was on purpose, but it was a suspiciously rounded amount. This has many different possibilities, one being that claims might have a designated multiplier, or that MA can instigate a manually ratio for a specific time, but not a specific avatar. So the next claim found on the planet will have this multiplier. (i don't not believe for a second that MA can give specific avatars multipliers, and i wouldnt play this game if i thought they did). Just more food for thought.