To be fair, you might get up to a scoring range of something like 166-174 or so, and then score on the bottom of your range on test day (thats what happened to me). Once you get up to about 168-170, I feel like the LSAT loses some of its predictability because you basically have a handful of really smart people duking it out for their place on a huge spread... remember, 172-180 is all the top ONE percentile. So yeah, it gets crazy starting around 170.
Also, you are supposed to score within a 6-point score band "95%" of the time, if I remember my stats right. So the 166 you scored might just be that 1/20 chance that you scored above what you were supposed to.
At any rate, great job though! I think my first diagnostic was 157... I worked it up to a 168-174 score range and got a 169 on test day.