Way out west, oya etc.
I personally think they should change the dates, as mid summer they miss out on quite a bit.
Big festivals like Glastonbury, Roskilde, wetchter early summer. Likes of pukkkelpop, creamfields and reading late summer.
Especially the days sziget are on, could pick up plenty of acts over those weekends.
From my recollection they have never sold out earlier than 1-2 days before the festival starts. However this year seems to be selling better than any previous edition. They will surely give some notice if they come close to selling out in advance.