Strong rainfall: pressure on domestic basis, CBOT also to fall but by less than here in Oz
Mild rainfall (enough for average to just below average yields): trading in a relatively narrow range, both domestic and CBOT. Look then to SAm lead, corn etc
Dry Spring/El Nino: mild to strong price rally, with larger moves domestically than on CBOT.
Your IG derivative would be based on CBOT, so probably more attention should be paid to those prices than domestic basis. While the Australian wheat crop impacts CBOT, unless the crop is significantly outside the median, the amount of surplus/shortfall supply hitting world markets is not as significant as many countries.
Also worth noting that the nation's biggest wheat supplier - WA - is looking very good and on-track for some handsome yields in most port zones.
