You mention a "method". I hope that is based on form analysis and not system rules because systems have a habit of falling to pieces and not recovering.
It pays to back on pace runners. If you choose backmarkers then you must get much longer odds to make up for the disadvantages - eg lack of pace, held up for a run etc. etc. When backing backmarkers it is always risky if there are not at least a couple of leaders in the race. Look at Bravisa today at Doomben. Sent out at a short price but had no chance.