Years ago, someone posted info on the list from watching the inside
of the WBX through a borescope (I think that's the right word) while
it was running.  They started with oil at a low level and added
oil.  IIRC, at about the mid point on the dipstick the crankshaft
starts hitting the oil in the sump.  That is what causes the unusual
frothing that you never want in your engine.  As they added more up
to the "max" mark, it got really wild in there with a great amount of
oil being flung around and air being pumped into the oil in the
sump.  Not only does the crank hitting the oil in the sump add air to
it, the resistance of it passing through even a small amount of oil
puts additional load on the engine.

I think there are several things we owners have learned about the WBX
over the past many years that are wise "adjustments" to the factory
specs decreed by the loved/hated German engineers who designed our
beloved Vanagons.  This is one.
Edward