Also, why do people with ENS breath much better with colds but still sound stuffed up? I still feel congestion by my ethmoid sinuses and upper nose which I assume is causing this.

The answer to this is very clear:
In ENS some levels of the nose have been abnormally enlarged (like the inferior nasal airway following inferior turbinectomy). However, usually (unless one had all their turbinates completely resected, which is very very rare), there are other areas which were not resected. Now, when there is a cold - the over all amount of airflow into the nose is restricted because of the mucosal swelling, but in areas where the turbinates were not significantly reduced or untouched then of-course, just like in a normal nose, there will be a sense of obstruction and stuffiness in certain areas of the nose.
For example, I had total IT resection, so when I have a cold I can get more resistance to my lungs and even feel my nose more, but I can feel that while my inferior passage is still letting through too much air (though feels more normal now) my middle and superior passages feel stuffy or blocked.
A nasal cold in an ENS patient - is just like having implants implanted in the wrong place - over all they help create back resistance and limit the airflow but they are located in such away which disrupts the normal aerodynamics so they offer some help while causing unwanted obstruction too.