Copper crush washer; which is better thick or thin

I have been told that a lot of the new copper washers are too hard. You can heat them with a propane torch and then let them cool to anneal the material somewhat. I ended up using some "good" used washers on my brakes when I had the same problem.
THIS!! THIS RIGHT HERE!!!

Also, tighten it some, tap the bolt with a hammer/ mallet, then retighten a couple of times, test, etc.