One feature of the business model behind big banks' fractured brands has become clear in recent rounds of negotiations with the Finance Sector Union over pay.Staff at Westpac Banking Group's St George, BankSA and Bank of Melbourne businesses will all receive a pay rise this year of 3.25 per cent, half a percentage point less than for employees working under the banner of the main brand.It's a similar story at Commonwealth Bank of Australia where staff working for Bankwest will also receive a pay rise of 3.25 per cent, still half a percentage point less than employees working for the main CBA brand.