I'm sorry. Us old people can't figure that kind of stuff out. 

 When I was at a yard a few years ago, they were telling my husband and I about the A, AA etc.  they were big rocks, not little at all. 
 I have pea gracel in there now. It has all sunk in.  Plus, the guy behind me insists that I have to have big rocks.  As much as I think he is just a jerk, his family does own a large dairy farm.  They are the owners of the stupid guineas that keep coming into my yard.  He really does know a lot about animals.   Though, that does not mean that he is right.  It does mean that he will refuse to sell anything to me if I disagree with him. 

 He charges more than the other landscaping yards around here too! 
 Anyway, I just want to have good drainage always.  As I keep saying, this is a now or never kind of thing.  I just don't see myself bringing tons of rocks in through the door later.