Skill levels in Phalanx XXV

[chesskobra]

I would like some clarification about the -e and -z switches in phalanx. From the Readme file in the Phalanx XXV source code, -e 0 corresponds to best play and -e 99 corresponds to the weakest play. From what I understand loosely, -z switch functions as follows (please correct me if I am wrong): if we specify, say, -z 30, then first each available move in a position is evaluated, and then the evaluation is randomised in the interval [-15,15] of the calculated evaluation, and then the move with best randomised evaluation is selected. It seems to me from https://www.chess.com/forum/view/chess- ... lanx-xxiii that the z parameter is used to interpolate the playing strength in the range from e=0 to e=1 (about 2400-1650 Elo according to the above link, but the actual numbers are not too relevant to me). But the z values in the configurations suggested at the above link (from z=1 (approx. 2380 Elo) to z=9 (approx. 1650 Elo)) seem very low to me. It seems that the actual weakening of strength is achieved by setting other parameters (-n nodes per second and -t transposition table size). Is it true that the z parameter is used only to avoid repetition of lines, and not really to adjust playing strength? Has there been some calibration of the z values vs playing strength, keeping the other parameters constant?