The 18pts now makes sense.
They seem to tell everyone to do Kickstart for the first couple of weeks. I assume its to almost guarantee a good weight loss and then you'll come back again (cynical, me - never...)
There is a calculation on one of the stickies - same one as in your books but you will be on more than 18 guaranteed - as it goes on weight, age, level of activity etc
It might be just enough to give you a little more variety.