This is not true; position/time are not quantized in the standard model. String theory is not canonical. I think a better way to think about it is not in terms of size, but in terms of time. A particle in a bigger box, on average, can go on a random walk for longer without hitting a wall. It will take longer for a particle to sufficiently (arbitrarily close) exhaust the phase space of a bigger box.
This is not true; position/time are not quantized in the standard model. String theory is not canonical. I think a better way to think about it is not in terms of size, but in terms of time. A particle in a bigger box, on average, can go on a random walk for longer without hitting a wall. It will take longer for a particle to sufficiently (arbitrarily close) exhaust the phase space of a bigger box.