I'm sure it was questioned in this thread, so here's "official" information from Diono:
https://www.facebook.com/DionoUSA/posts/1084155878303751
"Melissa, because our seats have a full steel frame, we allow the shoulders to go above the top harness slot when forward-facing (see page 33 of your manual). For your 2010 Radian she'll be too tall when she exceeds 53" OR when the tops of her ears are above the top of the restraint, OR if her shoulders are touching the bottom of the XTSL head wings when they are raised to their highest position." (emphasis mine)
That's all fine and dandy for them to say that, because they know their *seat* can handle the forces, but what about my child? If she's 1/2" above the slot, she will travel an inch before the harness catches her. If she's 1" above, she'll move 2", and then slam into the harness. When *every* piece of information says that the harness needs to be at or above the shoulders when FF, for every manufacturer, from all the experts and crash testers.... why would I take that chance? I've done so much to keep her as safe as possible so far, this doesn't seem like a good idea. I would rather have her in a booster, with the adult seat belt and it's locking retractor, than an inch above the top harness slot!
Just thought I'd let you all know.
Still waiting for the Harmony to arrive in Calgary: Selina has been told not to grow in the torso until it gets here!
Melissa