If you want to avoid heel clip you need with a good heel cutout profile. Square cut panniers are no good.
Then you need to mount them higher and further back than normal.
If you are using smaller panniers you dont need a special rack to mount them further back, just slide them back on the rack. Rixen and Kaul mounts come on a sliding rail.
Note some racks have doubled-up section of rod where you cant fit Rixen and Kaul style locking hooks. Avoid this style.