Hi Robin,

It should make a difference, but we do not expect it to be big.
And actually, why would aligning to any particular volume be
necessarily better than another from that perspective?

What we hope is that alignment to a different volume mostly
amounts to a constant shift among all motion parameters,
akin to offsetting them by the parameter difference between
the base volumes in question. And a constant shift in them,
per run or across, would have no effect on them in the
regression (it would be absorbed by the constant polort
terms).

So again, there will be some difference, but it should be
small. The advantage of using the min outlier is that it
should be more robust, since that volume should at least
not be corrupted by motion.

- rick