Bill
You prespray to break surface tension and in doing so, allow the vacuum to extract with the maximum amount of soiling while rinsing.
There is no likeliehood of the more heavily soiled area ending up looking cleaner, due to it being given more prespray than the surounding areas. You should feather in, the surrounds anyway !
I am well aware of the " correct " approaches and have used just about every product that's ever come on the market over the past 25 years.
No matter what I've used in the past 10 years I've never experienced resoiling problems, or wicking, although I've had to rectify a number of other peoples.
I believe the majority of problems are caused by overwetting and / or, to much chemical being applied. This is not necessarily due to low powered machines, but more likely to poor use of equipment and some people will never ever be good at cleaning carpets, suites !