Do beam-forming devices expect a particular antenna configuration?
There are two classes of beamformer. One type has the antenna configuration hard-coded into its mathematics, and attempts to construct geometrically beams towards wanted sources, and/or nulls towards unwanted sources. The other type uses general complex matrices to maximise SNRs of expected signals, and to the extent that it 'beamforms', the positions of the antennae appear implicitly in the operation of the optimaistaion during channel measurement.
The 'beamformer' in a MIMO WiFi base station is of the second type.
There may be second order effects if the algorithm used expects the antennae to be within a wavelength of each other, as would be the case in a physically small router. Widely separated antennae, although better than close antennae in some respects, have a larger dPhase/dAngle_of_arrival, which may potentially cause some training algorithms to arrive at sub-optimal solutions.