The trick is to get an "acceptable" figure up front that you agree is a reasonable target.
Whilst I don't do stocktakes in my PD I have to have objectives that are
<mind the business bull.... Bingo here>
Challanging
Strategic
Measureable
Achieveable
Realistic
Targetted
or CSMART for short
i.e. I will reduce sincidents to our Q by 20% by end of october through identifying repeat incidents and fixing root cause.
so if I was you I would ask for something like " I will control stock within a 0.75% loss margin" then when you get 0.5 you have exceeded their target and rightfully have evidence for asking for a rise.