How to reduce armor encumbrance by half

[jbearwillis]

I am trying to input a new armor into the shadowrun data files.
It is the Form-Fitting Body Armor:
When worn in combination with other pieces of armor, the
form-fit armor rating is added to the other armor’s rating (ignore
the rule that only the highest value applies in the case of form-fitting
armor). When determining encumbrance, however, add only
half the rating (round down) of form-fitting body armor to the
ratings of other armor when comparing them to the wearer’s Body
x 2.
I have it put in and it works except that it isn't halving the encumbrance and I was wondering if anyone had an idea to get it to work.
Thanks for any help.