I would personally look on forums for people who have done it and have pictures to prove it. If 17" rims do in fact fit, there is probably way too little room between the caliper and the rim, which is too close for comfort in my eyes.
The 2018+ 6 pot brakes should be similar to the 2006 STi Spec C Type RA-R, and 17" rims do NOT fit. The car's factory rim size was 18".