Ok, after sleeping on it, bending slate seemed dumb. I realized I had dmt'ed the slate a bunch, but didn't actually grid it. With the slate being so long, it would take just a tiny amount of dip in it to end up with the results I had. So I gridded it and yup, idiot. It had a belly in both x and y directions...just a tad.
Grid/DMT/grid/DMT/etc. grind on the Arkie a bit and voila, the polished part is clearly already reaching in further than last time. With this new finding, I'm back on the horse. Unfortunately, I had re-barberhoned it already, which put on some new scratches. ... Shewt. That 6 dollar lapping service sounds nice right now, but I see the light at the end of this tunnel now.
And by the way, yes, i have lapping film that will likely be as good or better, but I grew up in Oklahoma, and some of my best memories are from vacations in the Ozarks of Arkansas. It will be more neat to me to finish with a rock from around there rather than a machine-produced lapping film.
"Of a thousand shavers, two do not shave so much alike as not to be distinguished." S. Johnson, 1777.