Vetiver Hedges for Growing Beds

When I was researching clay pot irrigation, I accessed studies that outlined clay porosity, soil type and moisture spread relative to the amount of water in the terracotta chamber.
If Vetiver does indeed 'wick' I keep wondering how large and how broad that moisture zone could be.
Of course there are many variables: soil type and quality, depth of the water table, age of the Vetiver hedge and its root reach, the already existing moisture content of the soil, how much water runoff was captured by the Vetiver boundary, etc. Other factors are the microclimate effect of the Vetiver stems and the amount of mulch covering the growing bed as well as the planting density of the vegetables growing in the bed.
And, of course, microbiology as sponsored by the Vetiver.
However, I'm open to suggestions given the diagram sketch above.
I am trialing at various widths on sandy soil. 
I'd think 1 metre radius from the root mass may be a general and 'safe' distance for any moisture zone. Many field hedges border at some distance to control runoff, establish a wind break and encourage push/pull without encroaching on productive space.

Images of Thai trials offer a template: (SOURCE: TVNI)

It's a similar idea depending on the type of crop that way it works:
Peter Pitcher : Change is the only constant. Vetiver hedges widen as the get older. Ideal width will vary with crop and management (eg need to access the bed) dependent. I have various width beds and find 1.5M at planting convenient for management (I prefer to not step on beds). They do narrow considerably with time however. Papaya beds probably 2M? Bananas probably 3M. I am noting very localized marked increase in waterholding capacity and increased water table (?) levels (compared to a bore I can visually inspect in the same area.