SX Heat race line ups?

Seems to me in the past you never saw #1 and #2 in the SX points standings in the same heat race. They always seemed to place RC and JBS in different heats when they were 1 and 2, and then JBS and CR in different heats when they were 1 and 2. At least that is the way my old brain remembers it.

Now you have CR and KW in the same heat the past two weeks. What is the logic for the heat race line ups? Are they seeded by practice times? Random computer drawing? Drawing Clothes pins? Was it changed this year from previous years?

Just curious. Thanks.