So in this context the leaders are being over bet and the back markers are not being sufficiently penalized. A Loss of 28% POT on what are otherwise, as a group, break even and solid selections is very hard to overcome.
Food for thought when deciding which runners to back with your hard earned money.
A good form guide or looking at historical videos should give you an idea of where your horse will be placed in a race. More professional information or "race maps" can add significantly to your confidence here.