I'm sorry for the double post. I just noticed a mistake I was making, but I'm still a bit confused. My 3dttest++ command above should have been the version I've pasted below. When I fixed this, I now have no voxels that pass the correction for hpow=0, hpow=1, or hpow=2 when tested separately. However, when I run -ETAC_opt NN=2:sid=2:hpow=0,1,2:pthr=0.01/0.001/19:name=all:fpr=5 I get clusters that pass the correction. The help page says there is little reason for including all three hpows in a single call. Could you please explain that more? Thanks again and I'm sorry for the confusion!

3dttest++ -setA Int \
sub001 stats.sb21730_REML+tlrc.'[44]' \
sub002 stats.sb21750_REML+tlrc.'[44]' \
sub003 stats.sb21767_REML+tlrc.'[44]' \
sub004 stats.sb21824_REML+tlrc.'[44]' \
sub005 stats.sb21826_REML+tlrc.'[44]' \
sub006 stats.sb21827_REML+tlrc.'[44]' \
sub007 stats.sb21838_REML+tlrc.'[44]' \
sub008 stats.sb21840_REML+tlrc.'[44]' \
sub009 stats.sb21843_REML+tlrc.'[44]' \
sub010 stats.sb21847_REML+tlrc.'[44]' \
sub011 stats.sb21858_REML+tlrc.'[44]' \
sub012 stats.sb21862_REML+tlrc.'[44]' \
sub013 stats.sb21866_REML+tlrc.'[44]' \
sub014 stats.sb21873_REML+tlrc.'[44]' \
sub015 stats.sb21875_REML+tlrc.'[44]' \
sub016 stats.sb21876_REML+tlrc.'[44]' \
sub017 stats.sb21878_REML+tlrc.'[44]' \
sub018 stats.sb21889_REML+tlrc.'[44]' \
sub019 stats.sb22100_REML+tlrc.'[44]' \
sub020 stats.sb22104_REML+tlrc.'[44]' \
sub021 stats.sb22115_REML+tlrc.'[44]' \
sub022 stats.sb22122_REML+tlrc.'[44]' \
sub023 stats.sb22135_REML+tlrc.'[44]' \
sub024 stats.sb22144_REML+tlrc.'[44]' \
-prefix Int_CorrectedTogether -Etac -ETAC_opt NN=2:sid=2:hpow=0:pthr=0.01/0.001/19:name=h0:fpr=5 -ETAC_opt NN=2:sid=2:hpow=1:pthr=0.01/0.001/19:name=h1:fpr=5 -ETAC_opt NN=2:sid=2:hpow=2:pthr=0.01/0.001/19:name=h2:fpr=5 -mask group_mask+tlrc.HEAD