Shortcut to size: A few questions regarding rep range and weight lifted

[jwardmagic]

I have started the shortcut to size program and am loving it so far, but have a question.

When doing microcycles 1 and 2, if on the second or third set you don't meet the required 12-15 rep range with the given weight, what do you do? Do you drop the weight down so you can continue lifting whilst meeting the rep range 12-15, or do you just try your best?

Also, after consecutive sets on the same muscle group, I noticed I can't lift as heavy using that muscle as I would otherwise be able to. Am I not giving myself enough rest time or is it normal to be lifting very light weights if your muscles are fatigued? To give you an idea of what I mean, I used to do 36kg skull crushers for 10 reps (2 sets). With this shortcut to size program, after doing some tricep pull downs... the next set (skull crushers) I can only lift about 10kg for the desired rep range 12-15!!! Am I doing something wrong or is this normal?

I'd really appreciate your feedback and help.