The maths behind the table I posted is as follows:

Say you're top pick has a 20% strike rate. That means in a hundred races, it wins 20. OK, so how many does the second pick win? Well, it must win 20% of those remaining races, because in those races, where the top pick is not going to win, it is effectively the top pick of the remaining field. So, it wins 20% of them, which is 16 of those 80. So, with your top pick winning 20%, your top two will win 20+16 = 36%. So, your third pick will therefore win 20% of those remaining 64 races, because neither the top nor second pick will win those, so it is effectively the top pick of the remaining field, and your top pick wins 20%. So, 20% of the remaining 64 = 12.8 (rounded 13) wins. So, your top, second and third selections combined win 20+16+13 = 49 races out of a hundred. Ipso facto your fourth pick wins 10 races, giving you a total of 59% winners in your top 4 if your top pick wins 20% of the time.

If your strike rate for your top chance compared to your s/r for your top 4 doesn't work out as the table suggests, then you must have a mic of rules which means that the more favoured market runners come out on top and the less favoured ones third or fourth, or vice versa if it's the other way.

That help?