I'm just a humble approach bloke, and no doubt the en-route magicians will correct me if I'm wrong. If memory serves me the vortex wake separation required is 5nm if crossing behind, or in trail, at the same level, otherwise minimum of 1,000' below (assuming the other a/c is a "Heavy".
Having said that there are a number of well documented cases of vortex wake affecting aircraft up to 2,500 ft below. It all depends on the ambient air conditions I'm told. Scant comfort when your aeroplane rolls over and hits you!