Analysis For Office (AFO) Combine function between different source systems

[#1]

Hello, I tried to exploit the combine function of Analysis for Office to link one dimension belonging to queries of two different source systems. In particular, one source system is S4 and the query is built on top of an Open DSO and the other is BW4, where the query is built on top of a Composite Provider. The dimension to be linked has been mapped with the same infoObject in the two systems but the Combine function is still not available. Am I missing something? Thanks