a) I wonder if one can learn from the "Kamashma' lan" of the Gemara in Nedarim to Keriat Hatora, Keriat Shema, tefila, etc. If someone said "ee anaochi metsaveach hayom", "hashem ae echad" or similar, that he must repeat the Pasuk again, and we are not saying that we are going according to what he meant to say. I'll be happy if you have any references.
b) The Ran (Mi'kam lishnah) explains that he made a long Aleph. How a long Aleph of "Ochal" can result in Ee Ochal?
a) Keri'as Shema has a requirement of Keri'ah, and therefore we clearly cannot go by intent. See Berachos 15b about the requirements for clarity in the verbalization of the words, that we must go by what we hear. (D. Zupnik)
b) As for your second question, it probably depended on the dialectic form of pronunciation at the time (for example, some Ashkenazim today would say "Oy'chal" for "Ochal," and a long "Oy" could easily sound like "Eeee"). (Y. Shaw)