Dear COMIS users

I am struggling with understanding the definition about link height
of vertical duct.

For example,
There are three rooms (H:3, D:5, W:5) in a row vertically.
Therefore the reference heights of room1, room2, room3 are 0, 3,
6m respectively.
I want to install 2 ducts like the followings;
duct1 : any diameter, length:3m, linking the ceiling of room1
and floor of room3.
duct2 : any diameter, length:2m, projected from the ceiling of
room3 like a stack

Then, what values are desirable for the description of each duct?
That is, "Height from", "Height to", "Own height factor".

If I entered <Height from :3, Height to :0, Own height factor:1>
for duct1
and <Height from :3, Height to :2, Own height factor:1> for
duct2 then the error messages were shown from cof file like the
followings.

***CER*** NOTE ***
&-NET-LINks: LinkID=duct_2 Type=DSduct_2 FROM(zone room3)=9.
m TO(zone ext_HS_1)=2.m deltaH=-7.m. ZoneHeight+LinkHeight is
different for sides FROM & TO, like a vertical shaft. Is this
OK ?
-----------------------------------------------------------

***CER*** NOTE ***
&-NET-LINks: LinkID=crack_1 Type=CRcrack_1 FROM(zone room1)=
2.m TO(zone room2)=5.m deltaH=3.m. ZoneHeight+LinkHeight is
different for sides FROM & TO, like a vertical shaft. Is this
OK ?

Is this OK really? I am not sure because there is no
description about it in the User`s guide. Please teach me..