Let me start by saying this information is based on Open Class races in Melbourne from 3rd July 2007 to 18th June 2011. The line of betting is taken from the Saturday Herald Sun Pre-post market. The total number of Open Class races was 569.

LOB....Wins....%......Total
.1.....189.5..33.3....33.4%
.2.......97....17.0....50.4%
.3.......77.5..13.6....64.0%
.4.......58.....10.2....74.2%
.5.......60.....10.5....84.7%
.6.......34.......6.0....90.7%
.7.......25.......4.4....95.1%
.8.......11.......1.9....97.0%
.9........7........1.2....98.2%
10.......4........0.7....98.9%
11.......5........0.9....99.8%
12.......1........0.2...100.0%

Interestingly,if you backed $1 on each horse on each line of betting (LOB) there are some lines which are returning a positive result.

LOB....Outlay....Collect......+/-
.1.......$637.....$681.65...+$44.65
.2.......$686.....$572.40...-$113.60
.3.......$713.....$533.70...-$179.30
.4.......$737.....$595.40...-$141.60
.5.......$754.....$882.10...+$128.10
.6.......$741.....$593.20...-$147.80
.7.......$656.....$529.10...-$126.90
.8.......$572.....$204.20...-$367.80
.9.......$443.....$255.50...-$187.50
10......$279.....$280.50...+$1.50
11......$167.....$312.00...+$145.00
12.......$97.......$73.50...-$23.50

The win dividends are based on Sportsbet Citybest+ i.e. best of SP and the 3 totes.