Farmland does only get hydrated by water 4 blocks away

Farmland does only get hydrated by water 4 blocks away

What I expected to happen was...:
I thought that 1 water source could hydrate a 9x9 field of farmland

What actually happened was...:
only the 4th row in the south of the water got hydrated and the other didn't

Steps to Reproduce:
1. Place water
2. Right click with a hoe on dirt/grass around the water in a 9x9 area