Issue with restricting users for creating PR for specific plant

Hi Guys

Need help

I am trying to restrict users for creating PR via ME51n for specific plants.
I have created a role with below org values
Purchasing group:XXX
Purchasing organization: XXX
Document type: xxx
Plant:001

Ideally this should allow the user only to create PR for specific plant 001,as M_BANF_WRK is having Activity 01,03 with plant 001

However the user is able to create PR for any plant, I have kept trace and  I found the below check.
M_BANF_WRK RC=0  tcode=ME51N;ACTVT=01;WERKS= ;type=TR;name=ME51N;

Any idea why it is not restricting at plant level...