Letters on Class B altitude indications on charts

I notice on the San Francisco TAC that there are letters next to the
altitude indications for the different areas of the Class B airspace.
I don't recall seeing these before on a TAC. The legend says only
"letters identify areas." The SFO TAC is fairly new; perhaps this
will be done with all TACs?

Anyway, I presume that this letter is given just to facilitate
identification of a specific part of the Class B when communicating
with ATC. Is this right? That would be the most obvious explanation,
I think. If so, does this mean that I would ask for clearance into a
specific sector of the Class B now?

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