x11prefix for the x11 environment

Hi all folks, I try to install some X11 components, but all the time "DestRoot" stop, because the files are available. This is true, because "DestRoot" try to link the files to "/usr/X11R6". My question, how to change the Directory. I try to change "x11prefix" in the conf File, but "DestRoot" use "/usr/X11R6" all the time. Thanks for any help, Lutz p.s. The default "x11prefix" points to "/usr/X11R6", not to something like "/opt/local/X11R6" ist this correct?!