But what about floor where they move all over? How do you get a fix on that?
The Jerk here…you figure out your exposure on different parts of the floor, calculate how many "clicks" of your selector wheel (for aperture or shutter speed) are required to adjust for the various parts of the floor, then roll the wheel up or down the proper amount. This is the same thing that's done when you shoot in a stadium where there are lotsa shadows and bright sunny spots.
The same thing is done when shooting, for example, on a basketball court where mid-court is brighter than the end lines, or on a football field where the end zones are darker than midfield (like where I shot last Saturday night)
The earlier advice that your AE can be fooled by dark or bright backgrounds is correct.