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Dear Guillaume and Torben,
Thank you for your help it was indeed the non stationary default flag that had affected the results.
This made me wonder what is the rationale of non-stationary correction. I can see the advantages for small sub-cortical structures. But when there is a large true cluster (such as often the cases with function-lesion mappings), locally it will always appear more smoothed. 
best

pia
From: Torben Lund [[log in to unmask]]
Sent: 07 November 2016 12:41
To: Pia Rotshtein
Cc: spm Parametric Mapping)
Subject: Re: [SPM] Cluster level correction SPM12

I guess this could be if you have changed the nonstationarity flag, in which case the critical cluster size will depend on the loca smoothness


Best
Torben





Den 7. nov. 2016 kl. 13.00 skrev Pia Rotshtein <[log in to unmask]>:

Dear Experts,
We are running a VBM study. We used peak-level cluster of p <.001 uncorrected, and 50 voxels.
What we found puzzling in the results table (which we never observed before) is that sometime smaller clusters are denoted as more reliable than larger clusters.
I took a screen shot to demonstrate the point:
<image003.jpg>
 
So you would see that clusters with 200 (highlighted cluster), or with 366 (first cluster) voxels are reliable at FWE and also as uncorr, while clusters with 507 voxels are not (the cluster just above the highlighted one).
So Our questions:
1)      Has anything changed lately in SPM12? 
2)      And also how can that be the case; I though SPM corrected for number of expected cluster which should be identical for all clusters in a given comparison/model.
 
Thank you
 
Pia