You bring up an interesting subject.
A11:A20 is named "rng1", and filled 1:10
C1 is named "rng2" and contains 50.
C20 is named "rng3" and contains 100.
=SUM(rng1:rng3)
Returns 155
=SUM(rng1:rng2)
Returns 205
Enter 100 into A1 and
=SUM(rng1:rng2)
Returns 305.
So, it really depends on *exactly* what do you want to do, as to how to
configure the syntax of your formulas, in relation to the size and placement
of your named ranges.