I have been continuing to work with Elly on the mat and we have worked up to a fairly consistent count of 15 for duration of her standing still on the mat. I have gotten a little fussier about how she stands as well, which I think is why we don't have more duration than that yet. Initially, as long as she kept her feet on the mat, it counted. But she quickly started to creep with her feet, closer to me. It was an inch by inch creep but it did mean that she was definitely not "standing". Initially I allowed it because I thought she was just adjusting for comfort but it transitioned into this creeping. Not only was it working against the purpose of the exercise...to build self control in her...but it also was going to affect my long-term goal of better trailer loading: I don't want her creeping toward me off the side of the trailer ramp.
So now I try to make sure she is in a balanced position before I begin to count, and then if she moves one foot even an inch, I stop the counting, re-position her, and begin counting again. I do count out loud. That seems to convey to her that we are working on something. If she moves, I stop counting and am quiet until she is re-positioned, then begin counting out loud again.