My 6th level Knight I just built with standard 13,000gp has an AC of 26, but only because I bought Bracers of Opportunity rather than a Amulet of Natural Armour. I had two builds one with a High Dex 16, and Con 12 and another with High Con 16 and lower Dex 12. Both ended up with the same AC as I put one in +1 Breastplate and the other in +1 Fullplate, just the one in the Breastplate could move faster.
Anyway it breakdowns as follows.
10+9 (+1 Fullplate) + 3 (+1 Heavy Shield) + 1 (Shield Specialization) + 1 (Shield Block) +1 (Dex 12) +1 Ring of Protection = 26
So Flatfooted 24 and Touch AC 12.
Shield Block is like Dodge but for a shield user so technically it isn't a fixed bonus so AC 25.
He has Combat Expertise as well, so possible 31 (33 Fighting Defensively), easy pick up items for more gold are increase the enhancement bonus of his shield +3000gp for +2, and an amulet of Natural Armour +1 (2000gp). I intend to level as a Fighter next level take Shield Ward and improve make it a either +1 or Versatile shield. That will make his Touch AC 17 (18).
This is probably a high AC type character for this level, but it wouldn't be hard to make it higher with different item choices.