[
Where is anyone here saying you need single-digit ES? Single-digit SD, maybe, but SD is very different from ES. In a Gaussian distribution, SD is approximately 1/6th of ES.
Actually, the estimate of SD is ES/4. And that will be "rough".
Then to get a realistic estimate of the real world variance, you should use at least +/- 3 SD, or to be even more certain, +/- 6 SD.
MM