Try as much as I did to get the Arkel Bug to work for me on my bike, no success. The only way to fit the bag so that I've enough heel clearance is to position the cam hooks so that the bag is way way back on the rack, but the bag is so far back that a medium-heavy load makes the front-end feel very light and the bike's handling didn't inspire confidence at all. Also, the hooks were so close together that the bag's weight is concentrated on a relatively small area of the rack.

It's a shame as the Bug is a nice bag, even though it lacks a few things I'd have liked.

I have found a suitable bag for my commute, the Ortlieb City Bag 2, which is angled to avoid heel strike and didn't require much adjustment of the mounting hooks to provide around 4cm heel-clearance; it also uses the QL2 lock system which works much better so that the bag is secured at three points on the rack. It isn't quite as roomy (21 litres vs the Bug's 25) or as versatile as the Bug, but it can take my paperwork , some bits and pieces and a change of clothes, and it's waterproof without needing a raincover, so it suits me well. Also, because it's quite a short-height bag, it works fine on my Dahon folding bike, which was the main reason for wanting a bag that could convert to a backpack so I could wear it when riding the folder.

Thanks to all who replied to this thread and provided very useful info, I've certainly learnt a lot about what to look for in a rack and panner/bag and hopefully this (pedantic) thread will be useful to others choosing a rack and panniers for their bikes.