Here are some details, and in a subsequent post to this one sometime after the scan has completed I will post the GNUPLOTTED results.
(SAMPLE TEST RUN)
(First Results - not impressive)
Setting the z-range (set zrange[-55:-35]) basically 'filters' displayed results by chopping off the low-lows and the higher than average highs (spikes) so that your eye can see the most subtle patterns or weaker changes.
Unfiltered with the zrange (dbm range)