I agree, except jhammond's Iron Cross (older design of wheel) is absolutely the hardest wheel I've come across to mount tubeless tires to. And the bead jack - though a useful tool - I don't find particularly helpful in this one instance. For the exact issue the OP mentions in having the opposite end of the bead slip when you try to brute-force one end over. And with the bead jack, I find it hard to mind both ends simultaneously. Maybe some are good at one-handed jacking. I'm not so good at it.

I just the center-channel method and carefully work it around until you're down to that last 3-5 inches where it gets really hard. Then I keep one end locked in place with a thumb and start gently "persuading" the other end carefully with a good tire lever. Don't get too greedy and try to brute force that whole section at once. Just work at the ends.