Westpac has flipped another card in a bid to revive its anaemic mortgage business by loosening the household expenditure benchmark it uses to assess investment borrowers.In a notification to brokers on Wednesday,  the bank said it was overhauling the formula used to determine the Household Expense Measure band for investors.Under the previous policy adopted by the bank in May, borrowers reporting lower living and property management expenses than those implied in the HEM benchmark were assessed as if their living costs were higher.However, Westpac told brokers that an immediate impact of the changes, which took effect on Wednesday, would be to increase the borrowing capacity of investors who already own an investment property."As a result of this policy change, your customers may experience an improvement in borrowing capacity," the bank told brokers."In particular, a customer with an investment property or looking at purchasing an investment property who is currently reliant on HEM (that is the customer's declared expenses are less than total HEM expenses)."Westpac CEO Brian Hartzer conceded on Monday that the tightening of lending standards in May of this year had been overdone and had forced brokers to deal with a system that was clunky.The bottom line effect of the May changes was to compound the market share losses of the last year because brokers found the bank's lending policies difficult to grasp.Westpac reported home loan growth of  only around 1.5 per cent in the 12 months to the end September compared to a system growth rate of 3 per cent."Some of it has been self-inflicted through the changes that we put through on the expense categorisation and the tool that we put out there - that we feel we've fixed," Hartzer said on Monday."We're seeing the application volumes increase again."So, I think there's no reason why over time we shouldn't be growing at or above system in our different businesses."Hartzer's comments were a strong indication that the excessive tightening of the bank's lending rules were of its own making, rather than being mostly attributable to ASIC's diligent monitoring of responsible lending standards.The rejigging of the HEM assessment as it applies to investors is the latest in a wave of credit policy adjustments that Westpac has implemented since August.Last month the bank raised the loan to value ratio ceiling on interest only loans to investors to 90 per cent from 80 per cent.In August Westpac introduced a wave of policy and pricing changes, including rate discounts for borrowers taking out loans with LVRs below 70 per cent.One of the key changes to the bank's broking platform  due to take effect next year relates to the streamlining of payments to brokers.Previously, Westpac required brokers to prepare invoices before commissions were paid on mortgage drawdowns but the bank says it will automatically remit such payments from January.