I've made some more calculations of morning and afternoon shade effects, this time with the maximum PPFD capped at 1000 μmol m^-2 s^-1. That is, if the full sun PPFD were more than 1000 at the time, I have set it to 1000. I've posted the full analysis here.

I downloaded hourly temperature data for seven locations, then estimated the PPFD and what the relative effects of morning and afternoon shade would be, during the hours when the temperature was close to an optimum for photosynthesis.

Here's a look at temperatures for a few locations.

And this is a summary of what these calculations predict.

The full report has a lot more data and details, including a monthly breakdown of estimated PAR in sun and in AM and PM shade. Thanks to @insaneturf for suggesting this.