I only [generally] ever bet for the win on one horse per race now after 25yrs. or so betting on 2 runners to win and the odd period of experimenting with Dutching more than 2. Betting on one horse only per race has been the more successful period . I certainly put far more effort into my form study when I was younger betting 2 runners, than I do now betting 1 runner.

Perhaps it works this way: Your records show you win 1 in 3 races betting 2 runners to win and 1 in 4 races betting 1 runner to win. Therefore you are having 6 bets for 1 win versus 4 bets for 1 win. What you won't find in your records is that in races where you backed 2 runners you had twice as many wins as in races where you bet 1 runner to win. The laws of probability take care of that. The more bets you have with the odds against you the more you increase your loosing chances and the amount you might loose. Ideally [the mathematically ideal], your punting life would consist of just one bet only for the best price you can find.