Thanks for the input, especially that last blog post.
I went back and tried to remove as many variables as possible. I got the alignment ring back out and did that. I pulled out an old Step regular goalie runner - since we agree Step quality is probably the best - and sharpened it in the Sparx holder. And I ran 4 passes, per Sparx's recommendation, to adjust the edges. I tested in 3 places along the blade and it was all nearly perfect, maybe out by one click either way. So knowing that the machine was set to produce level edges, I took my Flare steel off the skate and sharpened it. Testing it out of the skate again produced pretty good edges, with a little more deviation. Lastly, I ran the other Flare runner in the skate, and tested it there. The results were all over the place. So it clearly seems that the problem was either with the sidewalls of the steel or the checker, or a combination of both. The Sparx is fine. The Flare Square is different than most others because it has a deeper channel and the top corner where the edge sits isn't square. I think the design was what was throwing it off because the Flare steel is worn down and may not have enough left to make good contact with the edge checker inside the skate. Either the set screw lands on the flared part, or the whole thing hits the holder.