Hmm, single letters that rhyme with other single letters are very challenging for recognition.
Since you already know the number of required quarters, something sneaky you can try is to have Q1 etc be the entire word, that is, instead of trying to recognize the combination of Q and 1, you will have a word “Q1” in your language model and you’ll edit the dictionary used so that the entry for Q1 reads as follows:
Q1 K Y UW W AH N
You’d do this for each quarter. Having the multiple syllable/sound combinations available for distinguishing between the quarters should make them recognizable.