we aren't talking about all the rocks in the universe, just the ones in the metaphor
The rocks in the metaphor were "rocks". Are you claiming that a rock in the universe is something else but a rock? Considering the amount of meaningful content in your previous posts, you probably do. Anyway, two rocks fitting together are not evidence of anything. As for eight rocks, let's see.
Two rocks fit together, therefore they once were one rock.
Two rocks composed of two smaller rocks each (four rocks) fit together, therefore they once were one rock.
Two rocks composed of the aforementioned rocks (eight rocks) fit together, therefore they once were one rock.
Eight rocks fitting together are in no way more evidence than two of them. In fact, they're the exact same situation, and since the amount of variations of how we can try to fit the rocks together rises exponentially, the probability of you finding a matching combination is raised as well. Thus, it can be concluded that it's actually a
lesser or equal (assuming it's quantifiable) form of evidence to that provided by two rocks.
Of course, the only numbers that will make logical sense in this case are 0 and 0.
EDIT: In case this explanation does not satisfy you, here's a simpler one:
http://en.wikipedia.org/wiki/Correlation_does_not_imply_causation