When you call a pro you'll get booked into the next available slot. With SB's there is a long dance so you need to juggle several prospects at once to insure any kind of regularity. Therefore you are going to get the clumpiness that comes from random grouping.

And part of that is reaching out to multiple POT SB knowing that a large percentage of them are never going to respond and that even then a large percentage of those who actually respond are going to flake, be overly demanding, or are simply BSC and not worth pursuing.  

 
The problem with "playing the law of averages" of course is the fact that luck can be a very streaky thing. You might have twenty POT SBs in a row all lead nowhere and then a week later ALL of them seem to work out, leaving you with the pleasurable dilemma of trying to figure out how to see ten different women all in the same week. lol

 
My "program" is to try to keep 4-5 regular SB in my rotation and I try to add one or two a month to make up for the ones I lose to attrition, but it's hardly a fool proof program, especially since I have a rather low "bull shit" tolerance level and the moment an SB starts getting overly needy, demanding or BSC, I drop her almost immediately, or at least cut back on seeing her to whenever no one else is available. I also never drop my SA membership since I live in "pussy Siberia" and I don't have hundreds of hookers to fall back on if I don't have any SB's to see, so i am constantly cultivating new ones. This tactic does lead to a lot of the "feast or famine" of which you speak.