Change from number of numbers to dimension

Instead of counting the total number of numbers in a bounding box,
use the dimension (which is half of the total numbers).

Change-Id: I13b02477663bf71b6ac626c0756c2b1c61c78d62
Reviewed-on: http://review.couchbase.org/39632
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>