> Asking them to imagine standing outside the house where they grew up, then walking to the kitchen and pouring a glass of milk. I have them rate their inner experience on a hand-to-hand scale for: color, sharpness, detail, focus area size, opacity/transparency.

A suggestion: Add in motion.

I'm decent enough at most of your list, but am almost entirely unable to visualize motion or (I believe related to that) living beings. In your example scenario, I had a point of view but no limbs - my visualization jumped between fridge -> gallon of milk -> poured glass, with almost no fluidity between the steps.