[split] (lack of) word groups

[MarcoP]

I now have a sizable corpus of medieval texts so it could be interesting to test this. Do texts really need to contain many repeating "more than three words" sequences in order to be real?

A sizable corpus will make things interesting.
Obviously, an inflected language like Latin does not have the same positional constraints as English.
In English you must say "I drink coffee" (subject, verb, object), but in Latin "Claudius aquam bibet" "aquam Claudius bibet" etc are all possible, since suffixes specify the grammatical function of each word.

Also, one should consider how much languages change with genre/individual style and time-period. For instance, Chaucer could write:
Ful many a riche contree hadde he wonne

Finally, spelling variation will also have an impact. Unluckily, almost all transcribed texts somehow normalize spelling.