Good SR averages Kenny. Unless you are backing fairly short priced runners, your making reasonable doh-ray-me $$$

I think the reason for your smaller than [mathematically] expected ROO prediction for larger races based on your SR in 6 and 12 horse fields, is simply due to the fact that larger fields are loaded with more rubbish horses.

What mainly counts is the 3 or 4 real chances [on average] that make up 80% winning chance in a 12 horse race, compared to say 2 to 3 real chances making up 80% of winning chance in a 6 horse race. The number of winning chances are not halved in a 6 horse race compared to a 12 horse race.

If all horses had the same chance in both field sizes, you would find a bigger ROO potential for a 12 horse field and would get a smaller SR. Considering the real winning chances in an average 12 horse field, your SR of 24.9% should actually be better. The reason it isn't is that more possible unforeseen events happen [having to run wider, bumping and less opportunities to come through from behind etc.] in larger races. So in fact the SR% in larger races look OK, but my seasoning and explanations above suggest they are not as good value as they look on paper and point too larger races actually being poorer value if you follow my drift[?].

9 to 12 runners is my prime field size pick for odds and confidence ratio. Above 14 runners is my cut off for perceived value. The SR's you have mention seem to support this logic I think, but in the scheme of things as far as your concerned, I'd just keep doing whatever you are doing.