Well, the tank was a bust. The development was uneven on the edges. I went back to a small tray, keeping in mind that touching the neg must be kept to a minimum, but this didn't work either. I am guessing NOT ENOUGH agitation this time because there were several lines in the neg corresponding to the ribs in the tray.
I was about to give up before I thought that the 4x5 drum I use with my Jobo CPE-2 might work. It is one of those which holds six negs in a reel. The advantage is that I can do all this in daylight once the tank is loaded and I don't have to touch the film at all. Since Diafine calls for only slight agitation, the fact that the Jobo tank can't be inverted is not a big deal. The Jobo tank worked just fine. There was no mottling and it was way easier to do. At some point, I may try the taco method also, although the Jobo, admittedly used incorrectly, worked great.
I figure that for sheet film, Diafine is meant to be used in a tank with film in hangers.