Do you have the actual laptop dimensions? Are you carrying the case, or just the laptop?

Heel Strike may depend on the rack positioning & chainstay length.

I found a pannier set similar to this one (unfortunately I can't find brand markings on mine).

ROSWHEEL Bicycle Waterproof Travel Pannier Rear Seat Detachable Trunk Bag | eBay



Mine was able to fit a pizza box in the top(trunk) bag. If you got the bag above, you could customize it with some padding (if it didn't fit your laptop case). It looks like the top detaches and makes a nice shoulder strap bag.

You may also just take your laptop to a bicycle or sporting goods store and try it out.

In the past, I've carried a laptop in its bag slung over my shoulder/back, and it worked reasonably well.