I had a similar issue with index size after upgrading to version 6.4.1 from
5.x. The issue for me was that the field which caused index size to be
increased disproportionately had a field type("text_general") for which
default value of omitNorms was not true. Turning it on explicitly on field
fixed the problem. Following is the link to my related question.  You can
verify value of omitNorms for your fields to check whether this is
applicable in your case or not.

On Tue, Feb 13, 2018 at 8:48 PM, Howe, David <[EMAIL PROTECTED]>