This may be due to the fact that the r0 and r1 of the text <plot> block are limiting where the labels can be drawn.
If you're not seeing anything at a radius larger than r ~ 0.95r, then try defining a generous space for the plot, e.g.
r0 = 0.7r
r1 = 1r
and see whether that resolves it.
If that doesn't help, zip up your conf and data files and email them to me
mar...@bcgsc.ca and I'll take a look.
m