The strength (stiffness) of the limb at any point will effect the tiller at that point (except maybe the last few inches of the limb).
The strength of the limb is proportional to it's width and proportional to the cube of the thickness.
We usually adjust the thickness to adjust the tiller, but adjusting the width also has some (rather less) effect.
It's your choice, if you want more bend you must reduce the thickness or width, or a little of each!
I'd get the brace a bit higher now too as it will effect the tiller, say get it up to 5".
If you hold a CD (or saucer, mug etc) up to the pic , you will see the bow has a nice arc of a circle curve over the inner half of each limb. the outer half of each limb isn't bending much. Ok you can't get the last few inches to bend but the outer half need to do some work.
here's a pic with an arc of a circle on it.
Del