Hi David,
I thought that using quotes around the string I want to find at the start of the filename had fixed the problem but there are still anomalies in my search results
Unfortunately, it appears you've hit a case which is outside the original design of our search engine, which operates at the level of keywords or quoted phrases, rather than at the level of positional matching of substrings or spans-of-characters within a word.
I've added an issue to our project tracker to research adding the missing functionality.
I don't have a great workaround in the meantime. Best I can think of is to use an unquoted anchored search, like
filename ^n12 and then sort by filename, so that at least the results starting with "n12" will be grouped together.
Sorry for the inconvenience.
-Bill