I have a Ballistic HC case and I have had a hard time with the Control center opening. I found if I tried swiping straight up it's never effective than if I do the arcing swipe described - start near the home button and finish the curve near the mid-point of the right edge of the screen. Thanks for that!
I think this is biased toward right handed users. Why not make it the area and movement as the notification center but from the bottom?
Finally! I have a method that work for opening the Control Center almost every time with my Otterbox Defender.
It is actually all in the amount of touch pressure.
In other words, if you try too hard... you'll never get it or you will frustrate the **** out of yourself.
Here is the key, if you use a SUPER LIGHT touch, it works! You don't even have to get your finger all the way to the bottom. Just take your finger and do a "Feather Like "swipe from the bottom of your screen and the control center will pop right up!
I struggled with this forever until I realized I was just trying way too hard.
Give it a try and let me know if I'm crazy.