How do I get ORD to recognize a prefix on a station equation?

How do I get ORD to recognize a prefix on a station equation?  your examples suggest that it should work, but I'm not seeing it.  If I include a prefix it ignores both the prefix and the requested ahead station, and sets the ahead station to zero.  Analyze point describes it with an R1, R2, R3 etc as a suffix, which is not what I asked for.  I want a back station of 2+00 and an ahead station of A 2+00.  How do I make this happen.  (inroads did it quite nicely)
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