simple plotting wcor (Rssa) question

Hello,
I try to plot w-correlation matrix of singular spectrum analysis by
using the package Rssa. This is an example:

 > library(Rssa)
 > s <- ssa(co2)
 > w <- wcor(s, groups = 1:20)
 > plot(w,cex.label=3),scales=list(at=c(10,20,30,40)))

However cex.label dos not have any effect. Also I would like to change
the tick labels, currently they show up as F1, F2 etc., and I would like
to have them as 1, 2, etc.

Any help would be very much appreciated
ingo