Just checked my database.

46% were lower then the price offered 10 secs before scheduled jump.
42% were higher then the price offered 10 secs before scheduled jump.
12% fell within the prices available 10 secs before the scheduled jump. So slightly higher then the back offer and slightly less then the lay offer.

Seems to be pretty random to me.

This was for AUS races only for the last 6 months.