I remember reading a few years ago that HRV actually have a structure and a plan as to the strength/type of each meeting on a Monday, Tues...Sunday etc. Might have been in a HRV annual report. I believe this is still the case today, many Thursday day meetings are actually $3000 races.
My 2c is the trainers would probably be aware of this structure and thus able to program for their horses a bit easier.