I planted 8 last fall and 2 came up this spring. Mine weren't too close--2 ft apart for effect. The bulbs didn't freeze. Not sure why I only got 2. I don't have enough experience to answer your specific questions.

help me with my math ;-)

I'm planning to put these in a centermass array behind a boxwood.

10 inches apart is the recommended distance

If I have a row of 4 10 inches apart

The next series of bulbs that is offset behing the 1st line of bulbs - I should keep them 10 inches apart as well, BUT from the 1st row, since it's not exactly behind the 1st row of bulbs but staggered, I can put them at 5-6 inches apart right ?

10--10--10--10

6 inches of space

10--10--10--10--10--10