What this means is, the larger the size of the rain shower head, the higher the water pressure required. This is because, the water must be able to fill the rain shower head quickly in order to get a nice steady stream of water. You don't want to experience only the middle part of the rain shower head coming out water.

I will be using a 10" rain shower head as well and I installed a water pump to ensure that the water pressure is nice and steady. Want it to rain and not just drizzle mar.