Yeah, it the problem with the 620t, but Discus are a fish that will adapt with the space in terms of volume of water as long water keeping regime is good.
A breeding pair even in the wild will only move a small distance from a territory and they don't relly rely on a 'bottom' territory, and therefore wont fight for it, as would multiple pairs of apistos/dwarves.
Chances are they would hunker down around the outlet down pipe or a cone if supplied, and spend their time housekeeping.
I agree though-The 620T is bit of a Tard_is though :evil: