I have an IX UQ and really it is all about the sealing up the ends. If you shift at all you have to re-adjust it. It is kind of annoying...I agree. but, in the land of DIY...you kinda get what you pay for
Here is a vid on how i set mine up...it has taken me to high 20's and i was cool, not cold but cool. 40's and above....works like a charm. For 20's and less I actually use my thermarest with the IXUZ....and then I am super hot. Like sleeping in the teens with just a t-shirt on.