Though the great majority of American speakers will use the same 33 runes to “spell” their speech, there will indeed be variations in dialect in how they spell the same words.
For instance, many speakers will “spell” the words cot and caught with different vowels (Os and Ore), while almost equally many others will use the same vowel (Os). Most speakers will spell pin and pen with different vowels (Incense and Elk), but for others, particularly in the South, it may be the same vowel (Incense). Such examples could be multiplied.
Much more rare, however, would be those for whom alternate rune names would be a better guide for the sound that the rune represents. One example would be Ether in place of “iggle” (Eagle) in Philadelphia English, where the main name may take the same sound as Incense for some speakers.
Still more rare than that would be speakers whose sound inventory would require additional rune-sounds to write the necessary sound distinctions. (See the page on Why Not the British Futharch? for an illustrative example, although others exist.)
The American Futharch is built with the flexibility for such variations that are part of the mystery of American language.
If your dialect is significantly divergent from General American (that is, along the lines of High Tider English, but hopeful not that divergent!) and you want to try these runes with it, Eirik would be interested in hearing from you.