It can be seen from the figure that, if very similar sentences (0.4-1.0) can be found for the testing sentence, using only 1 similar sentence can greatly improve the performance, using more does not provide further help and may even degrade the performance.
when the found sentences are not very similar (0-0.4), the improvement brought by fine-tuning is much smaller, and using more sentences, such as 16, is better than using one.