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Rick,

The -3 db beamwidth of a 4-bay antenna generally is between 40-70°, depending on frequency. A spread of 90° is unlikely to be covered satisfactorily by a 4-bay. Our DB4e, for example is down to around -5 to +5 dBi gain at 90°, again depending on frequency. You can expect almost any 4-bay antenna to behave similarly.

For stations at or near 90° to each other, you're usually better off with two identical antennas combined (splitter & identical coax leads) and mounted at 90° relative to each other ala our DB8e. Your results will still "vary significantly", but that arrangement offers the best compromise available. After that, a rotor is recommended or someone can try one of the "omni-directional" antennas that claim to receive from all directions. The combining loss of the two antennas is much less than the reduction in gain from being so far off boresite.