I hope you don't mind me saying this but there is form analysis and there is form analysis. It may well be that many of those losing horses at around $2.50 to $3.00 should only have been backed at around $5.00, so you may have really been taking unders.
Many horses around $8.00 are very poor value, but because the odds look generous punters also take them.
If those short priced collects are tote collects you are losing out big time. Go to http://www.propun.com.au/bookmakers.html and check out the tables. They are updated weekly and are a real eye opener.
DAS are brilliant with their DiviPlus for most longshots - best tote odds. But if you want to bet top fluc you must make sure not to have 5% or 10% of your winnings deducted whenever you back a winner. It is a competitive market however.
One other thing - have a look at the punting tips on this site in Punt to Win. Again, it's great value, and they are free.