If you are dictating with a timing, then read through the item first. See where long syllable words are. then look for the phrases, if there are a few brief forms, etc., which means you could say more words. With phrases, you can keep those together instead of splitting them up, so you may say "I will be able" as one carry and then continue with the next few words. Of course some speakers will break up the phrases, but you should think of phrases as wholes.
Shorthand writer is at 200wpm. Speaker varies from 150-280wpm, as most people do, especially when not reading straight copy. As the speaker slows down, the writer can catch up. If the speaker did not slow down soon enough the shorthand writer would have a hard time keeping up, but most of the time, people take pauses or talks slower.
"Gregg Shorthand had achieved the most extraordinary success ever attained by any system in the history of shorthand." John Robert Gregg, 1922