Can't answer your question Lew, but it does touch on some research I did a few years back. The result is, I disregard any contender that was not within 3.5 lenghs of the winner last start, (0 of course means it was the winner)

Also as a matter of interest, the same applies to any contender set to carry more or less than 3.5 kg's than it was set to carry last start. (I ignore app. claims)

These filters, keep me off many unplaced runners!!