Well I won't bail out and not make an effort to help, but like it has already been said here, improvements often mean less bets. If more rules [filters] are put in to improve SR, that's what will happen.
The only way to improve the system is to experiment with changes to rules. One change at a time to see the effect.

So as I understand it, the system requires a horse that has had 5 starts [6th up], won it's last start and won another. That's 2 wins well into a horse's current prep. of say 8 races. Most trainers would be very happy with that and unless the horse is something special, to expect 3 wins from an 8 start prep. is a bit over-optimistic but that is what your system is looking for, another win?
The system rules in this area don't seem to make a lot of sense to me anyway. For starters, a last start win is going to guarantee a low starting price and more weight, unless the horse is stepping up in grade a fair bit.

Most trainers set a horse [depending on age usually] to win 3rd, 4th,or 5th up because that is where peak fitness will be, especially in sprint races. From then on the horse's fitness is mostly downhill. Not always but mostly. Your selections kick in at the 6th race [?]. This is an area I think the system could be improved. Perhaps targeting 4th. or 5th. up rather than 6th. up.