It was based on initial qualifying, which set "region priority".
The fastest driver in initial qualifying was Serrano (EMEA). Discounting all other EMEA drivers, the next fastest was Fraga (NCSA). Kokubun was the fastest in ASOC, but slower than Serrano and Fraga so ASOC was the slowest of the regions.
In the final and the repechage the grid was staged as the lead EMEA driver, then the lead NCSA driver, then the lead ASOC driver, then the second EMEA driver and so on. That obviously started from 4th in EMEA regional, then 4th in NCSA regional, and so on, for the repechage, and the three repechage drivers would start 10th, 11th, and 12th in the final.
In fact Kokubun was only 11th quickest in qualifying, so starting the final third was quite the boost.