A MR74 with dipole omni antennas should be wall or mast mounted so the antennas are perpendicular to the floor. Dipole omnis produce a donut coverage cell. If you mount them parallel to the floor you're turning this donut on its side. That almost never is what you'd want for proper coverage to the devices at floor level.
How high are the APs mounted? Anything over ~25' you should look to use panel antennas instead of omnis. But, at a minimum you should first address the mounting orientation of the APs if they're as you described.
As for distance or coverage. That's a huge it depends answer based on transmit power of the radio, obstructions to the signal, and capabilities of the clients connected. I have customers using these outdoor with clear line of sight and you can get reliable high speed connectivity at many hundreds of feet. If there are obstructions outdoor or indoor the impact can vary by a huge amount.
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