I have borderline heel strike issues with my bikes & panniers. I've been able to finesse them adequately by:
- placing the panniers further back on the rack
- positioning the rack higher up and/or further back, within its mounting constraints
The ultimate solution is a touring frame, with longer chainstays. That way the weight is better distributed, instead of overhanging the rear axle so much. The mounting lugs are nice to have also.