I've had that issue as well. What I do is put aluminum foil on the entire sticky part so I can move it if need be. Then make a few 'rolls' of foil tape(like what you do with tape when you stick a birthday card on a present lol), and put that around the center where your probe would be That way it can adhere in the middle of the UTH as well. After that, just use foil tape on all edges and call it a day.
If you don't want to use the foil tape 'rolls' in the middle, just make sure the pad is really taut when you tape the edges. That works on all of mine, unless it's a super big UTH.









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