I often prefer to suppress the vertical cell headers in a ROWLATTICE (hard to read) and put in insets instead.

title "PROC SGPANEL with PANELBY statement";
proc sgpanel data=sashelp.iris;
panelby Species / rows=3 layout=rowlattice noheader spacing=10;
histogram SepalLength;
inset species / nolabel position=topright textattrs=(size=12 weight=bold);
rowaxis offsetmin=0;
run;