The number of unique values in the bloom filter will go up ~exponentially with n. So to control the false positive rate the bloom filter has to grow.
I tested this 6-gram "it won't find anything matching exactly", no match. Almost anything we write has never been said exactly like that before.
This approach is probably inadequate. In my line of (NLP) research I find many things have been said exactly many, many times over.
You can try this out yourself by grouping and counting strings using the many publically available Bigquery corpora for various substring lengths and offsets, e.g. [0-16]; [0-32]; [0-64] substring lengths at different offsets.