There really is no right or wrong answer in terms of the exact ratio....the more water the lighter the pigment. It's that simple.
Keep in mind these boots are almost like canvas material...if you've ever painted with water and acrylics on canvas then you know that water is your friend.
If it's too light make it darker...to dark, make it lighter...and add water for less pigment... works the same.
And the weathering is just that, very random, no paint by numbers here..
..REF PICS REF PICS!!
I hope that helped???:facepalm