Why MINIMUM 17" counter depth for clearance?

[Yikes]

ADA / CBC 11B-305.3 requires 30"x48" ground clearance for maneuvering. For example, a washing machine would require a 30"x48" parallel approach, centered on the machine. When I have an adjacent counter as per the illustration below, this parallel space can include knee and toe clearance underneath the counter per section 306, but here's the strange question: does the counter also need a MINIMUM depth of 17" in order to qualify the 30"x48" clearance at the washing machine? If so, how does having a minimum depth on the counter (as compared to no counter at all) help the use of the washing machine?
(I only want to use a 15" deep counter, for other reasons.)

The illustration below is a composite of two CBC figures to illustrate the point.

 

[mark handler]

 

[Yikes]

Mark, thanks but perhaps I'm not explaining my situation well. See illustration (plan view) below: I'm trying to fit a washing machine (pale red) and a shelf into an existing space (black lines are walls), and I only have enough room for a 16" deep shelf/counter (pale blue). The toes of the wheelchair will extend under the shelf. Is that OK, even though the shelf is only 16", instead of the 17" minimum?

 

[mark handler]

Make it a folding shelf and it cen meet the minimums