I'm not sure why this is, but I get heel-strike on just about any pannier I put on my bike... at least for the first 1/4 mile. Then, somehow I make an adjustment, and everything is OK.

There are two adjustments: 1) kick the pannier hard with your heel so it moves back at bit; 2) angle your foot a tad so it misses the pannier.

Having said that, I have a number of pannier bags that look scuffed up on one side. I guess I have it adjusted so my heel just barely grazes the bag.