I loved this breakdown. I thought you'd be talking about the equation that stipulated that happiness was a function of novelty, although your equation does sort of take that into account, with "expectations". Clearly, you expect what you have previously experienced, not something completely new, thus any positive novelty would have to increase the numerator.

I also like how you specifically referenced this, not only to happiness, but to a particular type of happiness. Great job of defining the scope of applicability.

I've written a piece about joy versus happiness, and some of the components of what constitutes joy, which come down to your worldview, your understanding of your place in that world, and your value judgements. I'd be interested in your thoughts if you'd like to take a look.

https://medium.com/dancing-elephants-press/two-paths-to-joy-c3320b6e4fa4