Interesting, it seems targeting the shorter ones seem better. It cuts a lot of the action out but here are the figures for SP $4 and less

WIN PLACE QUINELLA EXACTA TRIFECTA FIRST FOUR
Races Bet: 216 216 216 216 216 204
Races Won: 47 117 52 27 15 9
S.R./Race: 21.8% 54.2% 24.1% 12.5% 6.9% 4.4%
Outlay($): 216.00 216.00 1108.00 1108.00 4600.00 13800.00
Return : 136.80 177.04 877.60 766.00 3308.80 7934.80
$ Profit : -79.20 -38.96 -230.40 -342.00 -1291.20 -5865.20
% P.O.T. : -36.7% -18.0% -20.8% -30.9% -28.1% -42.5%