The way they are currently set up the bottom shield is in front of the shield above it, so that when it gets pushed on it is supported by the next shield (which is again supported by the next shield, and so on).

It feels more intuitive that the shield should overlap the other way (instead of the top of your shield being supported by the next shield, the bottom of your shield would be supported by the previous shield) because the final shield in the row has to be the heaviest to hold and the first one is supported by the ground.