Well, that is one way to think about it. I find it is an individual thing. For me, for example, if I was going to rest 2-3 minutes, I would pick a weight that I was going to just finish in the first set. If I was resting less, it would be that I would make sure I was close to the 8 reps in the last set.
What you are doing is fine. Just know that you can keep using that weight and try to get those 8 reps in the last set.