OK. Let's revisit the exact language. I'll include the Handbook explanatory text. There is no mention of under or beside.
Under or beside are not included in "within a bathtub or shower stall" nor "directly over a bathtub or shower stall".
The choice of the word "footprint" in the explanatory text is unfortunate, as many associate it with the bottoms of their feet, or, the floor. . . I submit that it is the widest cross section extending from above the tub or shower stall.
I'm going to drop "shower stall" for the moment 'cause the really difficult part of this is dealing with tubs, and especially the absolutely perfect image that Bob has just introduced. That is:
If I mount a floor receptacle UNDER the claw foot tub, the receptacle is neither "
within or directly over" . . . it's that simple. The "space" is the space "within or directly over" the tub, but not beside, or near, or under, or directly under the tub.