When you write a word, the single characters of that word will also get pushed back the list so you don't have to write them to often.
Is there any possibility that this could also work the other way around. For example, if a word has two characters in it, both those characters where practised earlier, either in other words or by themselves, so the system reschedules the writing of this word for a later date.
This way you could spend more time practising the characters that you don't know how to write yet.