The Barker's strongly advocate breeding while the female is in shed (not while the male is, however). A combination of her pheromones and possibly her demeanor when in shed can lead to more lock ups even for shy males (Not to mention, when her eyes go blue she can't see the male...so if he's ugly this can work to his favor).
In fact, I have heard experienced breeders say you can JUST breed during females shed cycles and be set. This ties in with Brian at BHB have said, in that you want to get a good lock during each stage of follicle development which are roughly "book-marked" by shed cycles.
JonV