for this question. I will tell u dat... some jockey really are good at some "special" race course or distance.

but its not the main factor of ur pick of horse.

as moss's age not young anymore. so he will ride so "safe" in the Happy Valley.. dats why his result seems not really good in HV.

But when some horse if he train it for long time or seems dats the trainer special ask moss to ride in HV. he ride his best and have good result in HV.
especially some class 5 horse.