Mike (and All),
I have to qualify my observation.
The multiple in-context relationships I described did survive the dissolving of the sub-assembly; however, the ability to modify them alternately thereafter (by toggling the active configuration) was only temporary.
Once the top level assembly was saved, closed and reopened, those in-context relationships became "orphaned".
Still my h> > Lo and behold, it's now possible to have in-context components