Um well, 1-tile shaft has a huge miss % actually.
The thing to consider is: is the increased miss chance so large that it offsets the fact that you can dig nine 1x1 shafts in the time to dig a 3x3 or four in the time of a 2x2? That is without even worrying about the 9x higher cost of the pickaxes.
If a 1x1 shaft has only a 20% chance of finding a vein, but a 3x3 has a 100% chance of finding a vein, then you're still better off (finding almost twice as many veins in an hour of prospecting) with more 1x1 shafts!