Yes, there might be situation where you can only decide between two unfair solutions and one is less unfair, and one could argue that that one is the reasonable choice. This is because reason-ability and fairness are not binary. Still, the tendency remains: if you say X is reasonable you imply X is fair.
Income per employee is not a good metric, you are right. However, if your profits are very high you must raise salaries if they are not already too high, lower your prices or invest to be fair.