Too much coronavirus time?

We’ve lived in this house for 40+ years and I’ve always thought the steps to the upstairs seemed steeper than the steps to the basement. I chalked it up to the carpeting on the upstairs stairway, but things didn’t change when we swapped out the carpeting for hardwood. Last week, I finally decided to verify the steepness of both stairways. (It was obviously a slow day in lockdown.)

I measured everything I could think of. Both stairways have 13 steps. Both span the same horizontal distance, so the upstairs stairway wasn’t cut short to make room for the hallway and the closet beyond it. The upstairs stair treads are actually 0.75 inches deeper than the basement stairs, so it’s not an illusion of wider steps, but the upstairs risers are also 0.75 inches taller than the basement ones and the angle of ascent is seven degrees steeper, proving that the upstairs stairway is definitely steeper than the basement stairway. Why, why, why???

After a few seconds, I had the Eureka! moment. The basement ceiling (to the bottom of the joists, not to the dropped ceiling tiles) is 6.5 inches lower than the main floor ceiling, so the upstairs steps need to climb 6.5 more inches in the same horizontal distance. Problem solved. Now, what shall I do for the next 15 minutes?

Next question: Is this true in other houses?