MongoDb $text search returning unexpected partial match

Question

I have a collection in Mongodb (ServerVersion 4.4.4) with several fields, of these fields I am interested in the following three of them:

1. denominazionePunto;
2. indirizzo;
3. citta.

From these three fields I have created additional (corresponding) array fields (indirizzoWords, denominazionePuntoWords and cittaWords) for startsWith searches as suggested in:

Efficient partial keyword searches

I did this because I know text index only support exact matching, so I created all the possible prefix string in the *Words arrays. E.g.: "citta"="Venice" => "cittaWords"=["venice", "venic", "veni", "ven"] (Searches are composed of at least three characters).

Additionally I needed to search on these fields with weights, so I created the following text index on my mongoDb database:

db.collection.createIndex(
    {
        indirizzoWords: "text",
        denominazionePuntoWords: "text",
        cittaWords: "text"
    },
    {
        weights: {
            denominazionePuntoWords: 10,
            cittaWords: 5,
            indirizzoWords: 2
        },
        name: "TextIndex",
        default_language: "none" 
    }
)

Following the advice on this answer to search for all the terms in a phrase:

MongoDB Text Search AND multiple search words

I performed the following find:

db.collection.find({
    "$text": { "$search": "\"via\" \"Roma\" \"essic\"" }
})
.sort({ score: { $meta: 'textScore' } })
.projection({ denominazionePunto: 1, indirizzo: 1, citta: 1, score: { $meta: "textScore" } });

I expected all the three string to be found as an exact match setting default_language=none, what I get is:

Partial Match for string "essic" but not as a prefix

How is it possible that the string essic is being found in Gessica and Jessica? It looks like it is a partial matching. Why searching for "$text": { "$search": "\"essic\"" } gives me no result at all? Non deterministic behaviours drive me crazy.

The denominazionePuntoWords for Gessica case is:

"denominazionePuntoWords" : [
    "gessica",
    "guerra",
    "ges",
    "gess",
    "gessi",
    "gessic",
    "gue",
    "guer",
    "guerr"
]

As you can see there are only prefixes and essic is no where to be found if not partially.

Thanks in advance