This morning I participated in a Rikti Invasion in Steel Canyon on Indomitable, and when the Rikti began teleporting in we all met up at Posi/Valkyrie. A low-pop server plus a non-peak hour meant that the turnout for the event was not impressive, so we weren't getting port-ins on a massive scale or anything, but enough that we'd occasionally get a Heavy Assault Suit.
What I noticed, though, was that the group was drifting away from the meet-up point, in the northeast direction, with each wave. The reason for this was because the Rikti were porting in only to the northeast of our group, and never in any other direction. We ended up getting quite far from the trainer by the end.
Was this just an incredible stroke of RNG? Given how many waves it was, my suspicion is that a bug might be hiding somewhere in the spawning code for that event.