Google didn't help finding a picture of a type of public bike rack that I saw in Holland, where every other bike is raised a bit so that the handlebars don't clash and so, more bikes can be parked in the same amount of space.
Here's what happens when all the bikes are parked at the same height:
The 2nd picture is of bikes parked in a Sheffield style rack, nose-to-tail. In N2T mode, the bars dont clash and every bike can be parked with the dirty transmission to the inside. N2T is just a user-convention but very few people realise the advantages or stick to it.