[GNC] Building 4.9 on ubuntu - install location

[M]

I am slowly learning the process of building Gnucash and think I am 
getting the hang of it.  My last build was Gnucash 4.9 on a fresh 
install of Ubuntu 20.04 in a VM (after some help on this mailing list!).

Per the instructions on

https://wiki.gnucash.org/wiki/Building_On_Linux#System_wide_multiuser_installation_locations

it appears that if I use the command cmake -DCMAKE_INSTALL_PREFIX=/opt, 
the software should install to /opt/gnucash.  Every time I build gnucash 
4.9, it appears to be installing directly to /opt.  If I use 
/opt/gnucash as the install prefix, it seems to install to /opt/gnucash.

Is this the normal behavior?  Am I misreading the wiki?  It seems to 
read that during building, if the install prefix is /opt it will install 
to /opt/gnuash.

Thanks!

Mike