The max dex bonus that applies to a tower shield is dependant on the max dex bonus your armor allows. Is that right? So say

Dragontouched Plate: 15 base armor 1 dex bonus
Dragontouched Leather: 8 base armor 7 dex bonus

The plate armor would only allow the tower shield to apply 1 dex bonus while the leather armor would allow 7 dex bonus assuming you found a tower shield with a dex bonus that high.

If thats the case why would any Defender of Syberys go for the plate set up? Using Dragontouched Leather + Leviks would get you 8+9 =17 armor and 9+7 =16 so 33 armor class. Dragontouched Plate + Leviks gives 15+3 =18 armor and 9+3= 12 so 30 armor class. 3 points of AC worse. Am I forgetting something or is the best armor you can wear leather armor as long as you can pump up your dex crazy high.