My suggestion is to see which words are being put in your OpenEarsDynamicGrammer.dic file which are not present in cmu07a.dic and look at the pronunciations that are listed therein and make sure that they are accurate descriptions of the way those words are pronounced. If they are not, those words will never be successfully recognized.
>At worst, we would like to have at least 60% accuracy (that is, 6 successes from 10 experiments). 80% and higher accuracy would be good enough.
Could you please tell me your current accuracy rate? It is improbable that you will get 80% for non-native speakers.
I would turn on logging (both verboseLanguageModelGenerator and OpenEarsLogging) and see if there are any error or warning messages.