Which combination of factors is most likely to produce a large value for the F-ratio and a large value for η2?

A large value for the F-ratio is most likely produced when there is a significant difference between group means relative to the variability within the groups. This can occur with a high treatment effect and low within-group variance. Similarly, a large value for η², which measures the proportion of total variance attributed to the treatment effect, is also indicative of a strong effect size. Therefore, a combination of a strong treatment effect and low within-group variability would yield large values for both the F-ratio and η².