The connection point must be present in all assembly variations in the same part.
Only configurations (*_asmcfg.prj ), not assembly tables, can be used.
The assembly has to be self constructing.
I.e., in the Rule properties dialog box dialog box, the Always build automatically must be set in every rule of the assembly.
(It is not possible to use the "normal" automatic build.)
In the Part properties dialog box dialog box, the Hide [Hide table] table checkbox must be activated for all parts, except for the dummy part.