I am having issues with Standby also, so will follow this thread.
When I first got the phone I could not get it to enter Standby. That may have been operator error.
After I did get Standby to turn on, I could not get it to stay on in a dark room. It would stay on in a bright room, but when the lights went out it would dim and then go completely out is less than a minute.
Apple phone support had me turn off Standby and Motion to Wake, do a hard reset, then turn Standby on again while leaving Motion to Wake off. Now it almost works correctly. My phone enters Standby, dims to red, and then turns off. Touching the screen turns the display back on again in dim red, and it stays on all night.
Except for having to turn the screen back on I’m satisfied.
I have a case open with Apple, so I’ll keep asking about the odd behavior.
Turning Motion to Wake on does not seem to do anything. The Phone will not wake to a hand-wave when in Standby, but it does not affect the transition to Standby.