I recently, for the first time, found myself snow camping on Mt. Hood (Oregon), not really thinking that I would run into that much snow at one of my favorite sites. 15 inches.
The weather was gorgeous, clear with temps in the 50-60 range and in the mid 30s at night. I was therefore sleeping on top of 15 inches of snow, on my Thermarest NeoAir "shorty". That's basically sleeping on ice! I use my pack under my legs. This was a first for me.
It took me a while to figure why, heavily clothed in my Western Mountaineering Summerlite, I was still chilly.
My butt was especially cold and I did have some 1/8" closed cell padding along. Not really figuring it out at 3 in the morning, I slid the doubled up pad (now 1/4" thick)under my backside. Wow! Instant warmth! I've read about this issue and really got a lesson in the practical aspect of sleeping on snow and ice.
The point is that the 2.5 inch NeoAir, having lost some of its inflation pressure, probably only had about a 1/2 inch loft under my butt. It seems to loose inflation as it chills in contact with the ground/snow. I inflate it hard long before bedtime so it can cool down and then again just before hitting the rack. Just as a point of information, I weigh 160 pounds.
I will be taking a torso length, closed-cell pad with me on the next trip out. The "experiment", I think, will lead to a more comfortable, warmer and better sleep for me.