Text field sizes restriction in *Forms.xml

[Vamsi]

    Hi,
                 My problem is when I am adding supplier to a product ,the size of the supplier product id text filed is restricting me from not entering more than 21 characters.But I want to enter more than 20 characters.I searched from where it is rendering,I found the form name AddSupplierProduct in ProductForms.xml file ,but there I didn't found any field with name  supplier product id

                   URl :  /catalog/control/EditProductSuppliers?productId="XXXXXXXXXXXX"
                           and my product is alpha numeric

 regards
 Vamsi