I DON'T use one, curved text is one of the reasons I don't annotate with LDT very much any more. I prefer to just make a piece of MText for full curve info and leader it in. When I need just the length I just make a middle justified piece of DText correctly aligned and positioned either inside or outside of the curve. It takes more time to create these labels but they can be copied and rotated about many segments of the same curve and I think they not only look better, but are much easier to edit if necessary.