There is no need to defoliate at all, if your plant would not need those leaves, it would not grow them in the first place!
Just remember, -
Maximum amount of healthy green leaves = maximum energy productionn = maximum growth.
It really is that simple!
Defoliating mid flower is really unwarranted, this is precisely when your plant needs maximum energy to grow the flowers.
Defoliation is not a necessary step when growing cannabis, it is hardly beneficial, except maybe in extreme over crowding.
Try and only ever remove yellow leaves, for by the time they are yellow, they have served their purpose.
The older leaves also act as "store houses" of pre-made vital growth elements (carbs, sugars, amino acids etc) that your plant will draw upon during flowering, as it is far more efficient to do so, rather than grow flowers and make those vital growth elements from new, at the same time. This is also the reason for the so called "fade" which occurs late flowering.
So, not only does defoliation reduce your plants capacity to make energy, it also robs her of this vital resource of pre-made growth elements she has so cleverly stored in her older leaves for use precisely now, during the flowering phase.
Therefore, I would urge you to seriously consider not doing any unnecessary defoliation of the large, healthy, energy making leaves.
Removing perfectly healthy, green, energy producing leaves and forcing your plant to grow new healthy, green, energy producing leaves seems like a waste of energy, energy that could be going into growing flowers, and rather pointless.
Hope this helps, Organoman.