If I'm switching my grip to hit the high up bottom it may as well be on top of the phone, it's perfect with the 4.7" iPhone but it is too high on the Plus model.
So you never lock your phone?
I let the auto-screen off handle locking in the vast majority of cases. I do also use Assistive Touch, so I can lock my phone with that. The only time I use my power button is whilst performing a hard reset, or entering DFU mode.