You probably don't want low Perception because, as an Unbroken, you want your engagement break penalties on enemies to hit in order to force prone. That's essentially the main draw of a fighter tank. Otherwise, engagement slots are rendered useless since enemies can effectively ignore you (and enemies in this game are keen to ignore the front liners from what I've experienced.)
Keep in mind, the reflex penalty is not tremendous especially when you factor in Weapon and Shield Style, large shields, and Paladin's increased defenses. Fortitude should be your lowest defense. Encounters are tougher since the new patch, so I'd advise against dumping Con.
Ultimately, you are unable to be the perfect Tank/Healer. You have to sacrifice something. I would not suggest maxing might because your effectiveness as a healer is thwarted by becoming a stationary tank. Paladin's excel at healing when they are able to close distance to party members and utilize Lay on Hands (base range of 3m). This knocks down your only efficient party heal to Exalted Endurance and maxing might for 1 extra HP per 3 seconds doesn't seem as valuable as forcing prones. With base might, your self healing abilities are fine because of Exalted Endurance, Constant Recovery, and Lay on Hands. You can also use your Lay on Hands abilities on melee range companions like Eder more effectively. Remember, Shieldbearers are about preventing death of allies, not necessarily healing them to full. Lay on Hands just allows time for a Priest or other dedicated healers/Second Wind to stabilize a focused companion.
This is, of course, only my opinion.
Edit: Corrections