I wondered about that.  That 'new' max fill mark.  Unless the top fitment of
the oil dipstick tube has been brought closer to the centerline of the
crankshaft, the distance from the centerline of the crankshaft to the
original max mark has not changed.  The max mark is there to detect/prevent
overfilling.  The engine has no idea how deep the oil pan is or therefore
what it's capacity is.  As long as the intake for the oil pump is submerged
and it's location has not been changed significantly from the original so as
to allow air to be drawn into the pump all is well, regardless of oil pan
capacity or depth.  Windage panels in the shortened oilpan keep the intake
submerged during extreme cornering in vehicles capable of unusual horizontal
g-forces.

Overfilling in a boxer motor can cause some problems insofar as reducing the
ullage volume.  (you knew you had that Funk and Wagnalls on the shelf for
something all these years, right?)  Excessive whipping of the oil by the
crankshaft can cause the foaming at the pump phenomenon as the oil is
whipped into a frothy state.  Can cause lapses in lubrication and the
associated screaming and moaning of various abraded parts in some cases.

The BMW Boxer (typ 246) afficionados recognized this long ago as
contributing to elevated operating temperatures and excessive oil
consumption.

Note that all scavenged oil systems have virtually no crankcase volume.
Some 911s, many british motorcycles, and many aircraft have scavenged oil
systems where the oil is stored in a tank that feeds the oil pump and
scavenged from the crankcase to fill the tank.

So better to be half a quart low than a quart over.  Check it and change it
often.

Moving that overfill mark may not be as good an idea as it seems at first.

pensioner (former typ 246, Matchless and 911S slave)