The lower the efficiency of the heat exchanger, the better?

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My IQ is a bit low; please help me figure out what’s wrong. For a heat exchanger, the outlet temperature of the circulating water is 48 degrees, while the outlet temperature of the oil and gas is 37 degrees. Target requirements: The outlet temperature of the circulating water should not exceed 45 degrees, and the temperature of the oil and gas output should not exceed 40 degrees (theoretically, the lower the better; however, in practice, as long as it does not exceed 40 degrees – temporarily – it will not affect the stable operation of the facility). How can the heat exchanger be adjusted in this situation to meet the target requirements? (The oil and gas volume is not adjustable.) By making adjustments, the outlet temperature of the circulating water was reduced from 48 degrees to around 45 degrees, while the outlet temperature of the oil and gas mixture was increased from 37 degrees to around 40 degrees. 1. Increase the water supply volume. Not feasible. Although both the circulating water outlet temperature and the oil-gas discharge can be reduced, the amount of circulating water used increases. 2. Reduce the water supply volume. Not feasible. Although the oil and gas discharge temperature has increased slightly (not exceeding 40 degrees), the temperature of the circulating water at the outlet is already 48 degrees, so it is no longer possible to reduce the amount of water supplied. 3. Improve the efficiency of the heat exchanger. Not feasible. Without changing the volume of oil and gas as well as the volume of circulating water, increasing the efficiency of the heat exchanger only results in a higher outlet temperature of the circulating water and a lower outlet temperature of the oil and gas ； Increasing or decreasing the circulation water volume does not achieve the desired effect while improving the efficiency of the heat exchanger. 4. Reduce the efficiency of the heat exchanger. Feasible. The heat exchange efficiency has decreased, the temperature of the circulating water at the outlet has dropped (from 48 degrees to around 45 degrees), and the temperature of the oil and gas mixture at the outlet has increased (from 37 degrees to around 40 degrees).