Yes, the rounded curve of the high point along the coronal ridge will be the first to offer resistance to mechanical extension of the penis. As you noted, this will be more pronounced when using the Corkscrew under full extension.
The elasticity of the materials should pose no problem going from flaccid to erect. The relatively short duration of the erection doesn’t pose much of a problem for comfort unless your fit is too tight to begin with. Constriction of the erection, to the point of discomfort, would be the indicator for a size adjustment.
When properly fitted, I can experience discomfort with morning erections of long duration. This will cause me to wake up and need to remove the Innerwear to fall back asleep again. This only occurs if I am layering the spandex sleeves or wearing the Sabre Skin on top of the Innerwear. Typically I sleep with the innerwear only or with well worn sleeves that are looser with a more comfortable fit as a result. If brand new, then definitely the Innerwear alone when sleeping!
Your mileage may vary so test and see what works best for you.