My Son is 6’5" and is OK on Strida with 18" wheels and extended handlebars [Bended (sic) bars] (both of which seem to add extra knee room). He had the seat right up, and also adjusted about 1" back on the plastic mounting.
He can also rode this bike without the extended handlebars - perfectly OK, once he accepted the upright riding position, with close bars.
There was something about this on the tips page on the US site (based on the smaller Strida 3) : strida.us/Tips-from-Mark.pdf