The higher the number the better. SoR has nothing to do with the current race. It's the competition each horse has faced over the last 5 races. Also, it has nothing to do with the performance of the horse in those races, just the the strength of those fields.
The reason we did it this way is to keep the number subjective. If we factored in performance of the horse, now we are not only competing with the Win Percentages, but telling the bettor what to play.
The SoR is especially strong on distance turf races, so look for that.
How much separation between two horses is considered an advantage?
It really depends on how the horse is performing against the competition in those last 5 races. Watch for maiden winners going up against winners for the 1st time. Their numbers are going to be lower because they have been facing losers. If you think they are on their way up, then you would overlook the lower SoR.
Example. If horse A has a 69 SoR and has been losing by 10 lengths on average and horse B has a 55 SoR and been winning, I would probably take horse B.