X-ray data is frequently plotted on an energy scale in log format. At the same time, the energy range of common detectors is only about one order of magnitude (e.g. Chandra ACIS .4 - 10 keV, XMM EPIC ...
Setting linscale=1.0/math.log(base) (which is < 1.0) ensures that the symlog transformation function is smooth, i.e. its derivative is continuous at the border ...