[papajam]

After refreshing my memory by reading this little ditty in the ATE brake manual, some pull-back is normal. After looking at the pic and seeing how pull-back actually works, it would seem to me that a hardened cal piston seal would pullback LESS because it's too stiff. This contradics a tech article (without pics) that I read many years ago which I now think was incorrect. But I'm with Roadtrip on checking the calipers anyway.
I'd check the rear bearings as well including axleshaft endplay. Endplay can cause knock-back in the rear calipers.
There are two ways I can think of (there's probably more) to determine if it's the front or the rear that's the problem. The first is to get an extra brake master cylinder output fitting and weld the hole closed to make a plug. Remove the line from the M/C that goes to the rear brakes, install and bleed the plug. If the brake pedal is now high and hard, the problem is in the rear. If the pedal is soft, it's in the front. This second method will require replacement of the brake hoses when you're finished. Take a pair of visegrips or similar and squeeze closed the brakehose to the rear brakes and see what the brake pedal does. Pedal high and hard? The rears are the problem. Pedal still soft? With a second pair of visegrips, squeeze closed the brakehose to the RF caliper. How's the pedal now? Use a third pair on the LF brakehose to isolate all the calipers if necessary.