There is a lot of variability in what may be wanted/needed. It will depend on bag size and shape as well as mounting position (fore and aft as well as up and down). Foot size, foot position on the pedal will factor in. The rider may prefer the ride characteristics of longer or shorter stays.
I never minded positioning the bags back a little to avoid heel strike with moderately short stays when I used to pack with 4 largish bags. These days I pack super light and can ride with a road bike with short stays since most trips I will be using some other bag arrangement than panniers.
I think the bottom line is that if you can avoid heel strike and the ride characteristics suit you all is well.