No, do not pay attention to fxsniper's post.
The puzzles are in the bits/keyspace related to the amount.
Like you said, #64 (.64 BTC) is in the 64 bit range: 8000000000000000:FFFFFFFFFFFFFFFF
sorry I use wrong word communication
key is on range puzzle
I mean you need to scan by use kangaroo jump too all area on keyspace but it is too wide
if need to focus on key position (no way to do) it have only random keyspace on keyspace to scan, may be it is wrong way to do this
yep, forget that I said help to not confused
see all puzzle that solve already that tell to know key is on bits/keyspace