To me, the intake manifold is a continuation of the
Cyl Head intake tract.
Look at a trumpet, it does not have any unneeded
discontinuities.
I realixe that, a one inch ID waterpipe could be
hooked up to a two inch ID pipe, and still flow some water,
but why bother.
Consider Holley intakes, the outlet sixes,vary.
It's not clear to my why, if, for some reason, the cross
section area of the intake needs to be different than
the area of the CH, that the best way to do that
is a haphazard connection at the intake-CH connection.