Frirst off, I don't put my wood duck houses in the water. The ducklings can jump and theis no cover for things like hawks 7 fish.
I put my posts on shore about 3-4' from waters edge, that allows for some grass/weed cover if the ducklings jump, and there are food sources like insects, etc. Most important protection period in when the chicks hatch an the are chirping for food from mama. This is a call signal to preditors.
I have 14 wood duck houses out ... some observations ...
You never need a baffle until you need a baffle. I have bluebird houses out where cats will figure a way to claw open the front door by pulling at the bent nails & screws. Once a predator knows there is an easy meal, they will attack until they reach the eggs or chicks.
The baffle holds off (in addition to cats) all the egg loving coons, & other varmits whole will tear apart the wood house. Also protects against snakes.
Overhead tree branches are also areas the predators will hang over and box on the nesting box.
I use 4"4" treated posts or 2.0" metal posts I drive 3-4' into the ground. Anything less and they will eventually tip from predator weight.