Mortgage aggregator AFG's latest market update shows that lenders continue to tighten their underwriting standards, with a reduction in the average loan-to-valuation ratio and a fall in the proportion of loans to investors.According to AFG's June quarter mortgage index, the average loan written by its brokers in the quarter was A$478,007. This is 3.9 per cent higher than the average loan size in the June quarter last year.While the average loan size has gone up, reflecting continuing growth in hose prices, LVRs have fallen. The average LVR for loans written in the June quarter was 69 per cent, compared with 69.7 per cent in the June quarter last year.Investor loans made up 34 per cent of mortgages written by AFG brokers in the June quarter - down from 40 per cent in the June quarter last year.AFG brokers lodged loan applications worth $14.6 billion during the June quarter, with 70.9 per cent of those applications for loans with major banks.The share of AFG's business with the majors has come down over the past 12 months. It was 71.7 per cent in the June quarter last year and hit a peak of 78.2 per cent in the March quarter 2013.