Virtually the whole seam allowance is trimmed away at the edge, about 1/8". Then the corner is clipped, again, about 1/8". With this trimming I was finally able to stitch the hem nicely across the seam. Previously I would find the hem bumpy or uneven or the fold wouldn't form properly at all. Success!
sewingrufflenarrow hemhemmer footclipping seam allowance