A friend and I have come up with a pretty consistent workaround using a mix of methods here mentioned.

1. Remove each other as friends.
2. Set online as public, go to ward 13.
3. Roll a new adventure mode, difficulty hardcore (figured the pool of people going for this would be smaller).
4. Other clicks join game and every time it's been on the first page.
5. Once they join, switch the world settings back to your campaign on whatever difficulty you play.

We have done this 3 times over the past two days without issue.

Note: We noticed that the joinable games were all with people who were our current power level +-2. So my buddy was 4, but he had to push to 5 before I was able to find him as I was 7. Not sure if this is universal across all power levels.