I took a closer look at my A520 pedals today. They
DO tend to hang down so that the back end of the pedal is nearest to the ground, but with variations on the angle - usually with the front end of the pedal between 30 degrees rearward and a few degrees forward.
Given that, I realise that my problem is that I have been trying to clip in the same way that I do on my double-sided M520 pedals - by stomping down with my foot. That usually won't work, unless the pedal just happens to be leaning forwards when I try it.
I adapted my technique... Instead of stomping down, I dropped my heel and approached the pedal from the rear and rolled my foot forwards. That seems to be enough to cater for the different angles that the pedals hang at. I rode round the block a few times practising clipping in and got to the point where I was nearly always successful without having to look down at the pedal.
Unlike
@Drago, I find that the contact between shoe and pedal top is improved relative to the M520s. It could be just the particular shoes that we use?