Thanks guys, thats what I thought after thinking about it for awhile.

If I were to lay a field, with 12 runners for 1 unit, I would get a return of 11 units.
Now, as long as the winner has odds of 11 or less, I would profit, yes?

If the winner has odds of 11 I would have to pay out 10 units, leaving 1 unit profit, right?

As the fav wins about 33%, laying the fav gives us a 67% S/R, so now to work out the odds needed.

Cheers
Mike.