I notice from
great circle mapper that BKK is very close to the midpoint of the great circle route between SYD and IST, despite the appearances on the map.
Initial headings for SYD-BKK and BKK-IST are very close to each other and also to SYD-IST nonstop.
Distance for SYD-BKK is very close to the distance for BKK-IST. Total distance is 0.4% more than SYD-IST nonstop.