Hi Luke. My understanding, if the 95% of the posterior distribution is above 0, we are reasonably confident that our variation is better when testing for an improvement. But when testing for a difference instead of an improvement, we can reject the null hypothesis if variation is extremely better or extremely worse, but in order to account for 95% of the distribution, we reject null hypothesis if either 97.5% of the distribution is above 0 (in which case the variation is better) or only 2.5% is above 0 (in which case the variation is worse then control).
That’s my understanding, but I need a validation that I’m thinking in the right direction. Thank you for taking your time to respond to my question!