HI.
I think this is not possible. The @root syntax only support direct attribute names of the logged in user, but not any srel references, like in @root.location.site.
One possible solution, which I used in the past, is to replicate the site value of the referenced location into a customized attribute of the contact record, lets say "zloc_site SREL site;".
It is relatively easy to implement a mechanism ,which, whenever the location of a contact gets changed, replicates the site value of the new location into the contact records zloc_site attribute.
A bit more is to be done , to handle the case ,that, whenever the site of a location gets changed, alle contacts of this location gets updated with the new site value.
I think enhacing this capability, so that @root references can also use joins,would be a perfect idea. I'll create one....
Regards
.............Michael