Further, there are a few other important variables:
1. the number hard attractions open during EMH hours has varied over the years. This summer saw an absurd cutback: August 2017 AK PM EMH was ONLY Pandora.
2. the ability to operate many attractions at partial capacity. Like only opening: one side of Space Mtn, one side of BTMRR, operating EE with fewer trains, operating boat rides (PotC) with fewer boats, operating the Speedway with fewer cars, etc. If fewer cars are running, lines are longer.
This year, Disney appears to have considerably cut back capacity during all peripheral hours (mornings, late night, and EMH).
3. Number of shows per day. For a time, HS had F! every night, then they cut back, then they brought it back. They also offer extra parades. HS also used to have the Christmas light show every night Nov-early Jan.
4. Extra soft attractions - these are things like street performers and pop-up character greets. On busy weeks, (roughly) the Main Street are of MK used to be flooded with characters. There's be some in front of the train station, more around the flagpole, another set by the Confectionary, and another set by the Plaza! The World Showcase was also s- sometimes- full of characters tucked into little back rooms and nooks. More than once, we saw a group of ten unusual characters ALL in the Italy area! It was awesome!
Other trips - as in more than once- Chip and Dale popped up, late at night- over by Space Mtn! Sometimes they goofed around in the arcade. It didn't matter that crowds were relatively low at that hour.
5. distribution of Fastpasses. I don't think any of us has any idea about these numbers, but even in the days of paper FP, it was clear that the numbers varied. the FP machines were sometimes completely covered. Some years WDW had FP during EMH, other years they didn't.
I'm sure there's more I'm just not recalling right now.
