... The highest AC in that party was Minthara in heavy armor (but no shield as dual wielder) with 25. Gale had 15 and Shadowheart 21. Unfortunately I can't reload the saves since patch 6 to see the details, I just saved a screenshot of the party at the time so I can still see the numbers but nothing more.
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Can you remember how you got to 25 with heavy armor without a shield? That's interesting. Maybe I could get Shadowheart with shield to 28 then? I'm currently in a modded playthrough with higher enemy hit chances and damage, a high AC as possible would be nice.