Straight from left field, who knows what the SP is going to be, before they jump?, answer...nobody. So trying to base anything on SP is futile. Over the years I have seen many horses that would appear set to start at say 6/4, return 7/4 or 2/1 because of a late blow, ie bookies trying to lay it, or something being heavily backed when half the runners are in the gates. And a lot of the time SP's are not really that accurate.