[phaker]

This depends on the distribution, for a uniform distribution all 16 hex digits are equally likely in every position.

Also for benford's law to show up you want your data to span several orders of magnitude (so e.g. you have numbers in tens, hundreds and thousands) and for a datapoint to be about as likely to give an n-digit number as a n+1-digit number, not everywhere and not exactly but it needs to dominate over there being ten times times as many of them with each step.