I said height, one of my first mantids did have quite a tall tank but there was loads of other stuff in there too like branches so she didnt have access so a nice bit of open space to dangle in when she wanted to shed.
I looked in one day and thought "hmmm, she's quite big, if she wants to shed she's going to be a bit screwed" so I moved alot of the branches out of the way. And I'm glad I did because that night she shed, I was fortunate enough to be able to watch much of process and she needed alot of height.
She needed pretty much her whole adult length plus forearms and back legs, plus the length of her old skin which was attatched to the roof by it's back legs and she was dangling from the bottom of it. She stayed there for most of the night while she dried out and then she climbed back up the old skin and went back to her favourite corner of the roof of her tank.
So im going to say that height is a must and width is a bonus.
Because she only shed within 24 hours of me moving the branches out of the way for her it got me wondering if the mantis has any concious control over when it sheds, or was I just lucky?