Hi
Have a look at Settings > Monitoring Options > Market Refresh > Display prices exactly as they are on Betfair website. It may be possible though this setting makes no difference, as I recollect there was some problem with this setting a while back.
Another thought is that if you are monitoring a market which has decreasing prices, and your refresh rate is quicker than the Betfair site refresh, you will see lower prices in MFP before you see them on the website.