Pardon my pedantics, but

Which shows that the array starts with 16 elements, and then doubles.

You've shown that with 10 elements, it's at 16 buckets. Trying this

c:\>perl -le "for (0..10){print qq($_: ) . %_;$_{$_}++}"
0: 0
1: 1/8
2: 2/8
3: 3/8
4: 3/8
5: 3/8
6: 4/8
7: 5/8
8: 7/16
9: 8/16
10: 9/16
[download]

shows that it starts at 8 buckets, and shifts to 16 buckets at 8 entries (though only 7 buckets have entries).