Hi Johnson,

I'm only a CONN user but I think I can answer your question. Usual whole-brain acceptable thresholds are p<0.005 or p<0.001 uncorrected at the peak level, with a cluster-wise FDR or FWE correction of p<0.05. If you use a peak-level p<0.05 threshold, as you have seen, you get huge clusters which, of course, survive cluster-level correction because it is statistically unlikely that such big clusters appear by chance. However, these massive clusters actually arise because you used an excessively liberal peak-level threshold, and they are furthermore not informative because they are very widespread and don't actually take advantage of the spatial resolution of fMRI.

Bottomline: you want to obtain small but reliable clusters, so use more astringent thresholds.

I hope that helped!

All the best,
Macià