Playing Angles on the Exchange

Someone recently described the following 'angle' to me.  Identify cheap speed prior to the race - horses who typically will lead at some point early in the race, before tiring and finishing far back. While the odds at or near post-time are likely to provide a fairly accurate reflection of the horses' chance of winning the race, it seems like that there could be inefficiencies in their odds as the race is run.  With Betfair's in-play wagering, there is an opportunity to take advantage of this.  One could potentially wait until the speed horse takes the lead in the race.  At that point, it seems likely that the horse's odds would overrate their chance of winning, and betting against them could be a profitable angle.  Note that this will only be an option at those tracks that allow in-play wagering.