It's not that it raises the water level. It doesn't. What it does is keep the water level the same but reduce the volume per flush. If you reduce the volume by adjusting the float you *DO* reduce the water level while reducing the volume. So the idea of the brick or milk bottle is to keep the first rush of water the same as before and get the @s#h$i%t& moving. Once it's moving it takes a lower flow to keep it going.

That's the theory anyway. I own no plumbing company stock, so I don't have a dog in this fight.