Another way of expressing the formula for the distance between two points is:

the square root of ((x2-x1)**2 + (y2-y1)**2 + (z2-z1)**2)

So plugging in your values gives:

the sr of ((0.246 - 0.0)**2 + (3.019 - 0.0)**2 + (9.617 - 2.021) **2)

the sr of (0.061 + 9.114 + 57.699)

which gives 8.178, so I'm not at all sure why your value of 11 works. Did you try it with a small f-stop number to see if it still works with a smaller DOF?