Hi Shaomin,
Seems to me that there are large variabilities within condition (e.g.
outliers and perhaps subpopulations?) Then I suspect the model fitting
might not be good. What is the PP(down-down-down) range for these
genes? Although they are top down-down-down genes, it's possible that
they are not classified with high confidence.
You may try to remove samples that are quite different from the other
samples in the same condition? You may also try to set the FCV to a
larger number, e.g. 3. Then the dynamic genes will be expected to have
FC >=3. By doing so you may be able to get rid of genes with moderate
FC and high within condition variations.
Hope this helps,
Ning