What BF price are you using ?

For example BF tote, BF SP or BF Weighted Mean, or a price you obtained on BF?

Each will provide a very diferrent result.

You have to remember the price you use may not be the price others obtained.

I do agree with you though that after commission there is not much difference with the favourites. To profit on betfair you really need to know your prices and where the value is.