Tried the Invacare matrix elite deep today with 6 inch contour. Good lateral stability without intruding upon your arms while providing greater shoulder mobility. Headrest and mounting hardware came with the back and were stable in full tilt/recline.
Not a bad choice. Much improved over my C 300 flat back. The new corpus ergo is probably improved over that, but I doubt it's as good as Invacare.
I'll be trying the J3 posterior deep lateral (PDL) next week, after which time a decision will be made.