It is known by most experienced trout fisherman that trout often suspend thoughout the season, making them tough to locate at times. Most fisherman know various conditions cause this behavior. On some bodies of water trout will suspend at certain times of day, then hug bottom at others.
One thing that often causes trout to suspend is often overlooked by icefishermen. This is the presence of a good population of Backswimmers and waterboatman. For those who don't know these are a semi aquatic beetle with a one year life cycle that are very important to trout in winter. You have probably seen these bugs swimming around while watching down your ice hole(sometimes they'll swim right up the hole). The backswimmers swim with their backs facing down and swim with oar like strokes. They are about 5/8 of an inch in length. They are usually olive or brown in color. Waterboatman swim with their backs up and are usually about 3/8 of an inch in length.
These insects have lungs and need to breath air. Hence they are restricted to the upper portion of the water column, as they need to get air from pockets on the under surface of the ice. Therefore active trout will often suspend to feed on them.
So if you're fishing just off bottom with no luck, and you see these insects paddling around, try fishing the upper third of the water column and see what happens. I bet dollars to donuts more fish will see your presentation.
Good luck!!!