As far as i know now that 4.0 is on rank arena works this way:

if you are waiting since less than 30 seconds you can be matched only with people within +/- 10 levels from you and within +/-1 rank.

if you are waiting since 31-60 seconds the level limit gets removed and you can be matched with whoever is waiting and owns your rank +/-1.

Every 30 seconds after the first 60 seconds widens the search range to +1 rank (so 61-90 seconds +/-2 ranks, 91-120 seconds +/-3 ranks and so on).