OP: the point of "down weeks" is to reduce overall stress to allow your body to adapt to the previous weeks' workload. the result is your body adapts into a stronger/more fit state. if you do not periodically allow for reocvery, your body eventually breaks down (i.e. injury). How you structure your down week is up to you, so long as your workload is below (60-70%) your regulary capacity. Don't overthink this, just take it easy. It is far better to take down weeks too easy vs. not taking them easy enough, same line of thinking as 10% under-trained > 1% over-trained.
New Question for everybody else:
After you have achieved a new high volume during your base phase, and you have maintained this volume for a couple months, are down weeks still necessary? This assumes that intensity is being held constant.
Thanks!