Initially mountain would suck gems only close to it, but that meant that in the late game when gems fly far and stack up near the stash, the mountain wouldn't reach a lot of them and would thus mainly suck up newly spawned gems from the air, which wasn't great. And you're right that gems in runner's hands are counted (unlike with bulldozers), which I plan correcting soon, but it isn't as simple, at least in terms of performance in the current system. But as I optimize the game more, the threshold at which mountain starts sucking rises, making it all feel a bit better.
However the real issue here is the late game scaling of damage force / Rune Of Power+War, which makes ores fly too far out (and gem geyser spam). I will soon be diminishingly capping and adjusting a lot of these systems.
