'small reduction' is correct and usable in written English.
You can use it to refer to a small decrease in size, amount, or value. For example: "The store was offering a small reduction on all shoes today."
The authors also found a small reduction in blood pressure in people who had more potassium.
This is a very expensive, unwieldy way to achieve a very small reduction in temperatures.
At best, corn ethanol delivers only a small reduction in greenhouse gases compared with gasoline.
But even a relatively small reduction in the interest rate can amount to a significant savings.
That rate reflected a small reduction of a preliminary tariff set earlier.
For gasoline, it takes only a small reduction in supply to trigger large price hikes.
Early in his Presidency, Obama did initiate a small reduction in our nuclear arsenal.
However, it is a relatively small reduction and, unusually, only applies to gas and not electricity.
This increase was associated with a small reduction in PaCO2.
The authors found no effect on HOMA-IR, but reported a small reduction of fasting insulin198.
We noted only a small reduction in SBP (~5 mmHg) after unilateral injection.
