Questioning EC (in General)

To start off I understand trained Dexterity offers no Encumbrance, am I right? Regardless, Ive notice in fights versus the Exbow and Axbow when I get a negative trained ST or DX I suffer no AC penalty. Yet when I get blasted by EC into the negatives I suffer an AC penalty. Why?

db vs The Lega (EC)

Upir cast Ethereal Chains on Dremora Lord (1,472,528)

Dremora Lord
Hit Points 8,586,457
Strength -363,118
Dexterity -641,442
Armor Class 457

db vs Cerberus(Axbow/EC)

Wolf cast Ethereal Chains on Dremora Lord (355,457)

Dremora Lord

Hit Points -229,506
Strength 752,598
Dexterity -6,395,492
Armor Class 458

db vs The Iconics 3e(Exbow/EC)

Ember cast Ethereal Chains on Dremora Lord (11,233)

Dremora Lord
Hit Points 6,625,196
Strength -290,165
Dexterity 817,460
Armor Class 458

1 ac? lol :P dude i'd be worried if you suffered like 400ac penalty :P

Enc is only affected by most pre-combat effects (A.S. excluded) but no in-combat effects.

EC is calculated pre battle, *xBow is calculated during. Thus you get the Enc before the fight actually starts.