The header rows must be explicitly referenced using a relative offset where 0 is the first row above data, -1 is the second, etc.
Since the function expects the header row(s) to exist you should precede it with a command to establish which header rows are displayed and in which order:
wks.labels(LUC); // Turn on Long Name, Units, Comments in that order wrowheight irng:=![-2]:[-1] height:=1.5; // Long Name & Units 150% wrowheight irng:=![0]:[0] height:=4; // Comments 400%