PRing again make it fresh in your inner mind, which has already done some work with it during the previous pass. However, your inner mind does more than just process what you PR. PRing again brings it to the top of the queue and repetitions makes strengthens your mental pathways for the material.
PRing a couple of chapters before and after has two good effects. The first it that material before and after is usually related, so that your inner mind has a bigger picture, in which to place the current needed information. The second is the fact that as you start the PR step, you quickly slip into the proper ALS. So you "potentially" poorest received material is the first few pages of any session. This isn't a problem after your familiar with ALS, but for some people it is an intelligent precaution.
Good luck,
Iam2 (I am not AlexK but I had two cents just lying around 
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