UPDATED(09/10/2019): See Below
The original is a great design, but the legs were flexing too much. They would move independently and not seat into the slots as well as they should.(Maybe the material I use has a little too much flex) So this problem made me want to fix it and I have added a brace between the legs and now it works great. It easy to use one hand now to adjust the angle rather than needing to use both to make sure both legs seat into the slots.
There is a bulge on the middle piece to accommodate the brace and the brace goes between the legs. The height is unchanged so they are still flat. I applied this to all 3 of the the latest models(v2.1). I also printed all 3 to ensure they work as displayed.
UPDATED(09/10/2019): Based on feedback modified the brace to be wider and the arch was stretched for better strength. Modified all 3 sizes and made 3 test prints. Seems to work well. Managed to add hex to wider arches which might actually add strength since more walls means more strength in 3D printing.
3D Builder was a fast and easy tool to make these modifications. Originally I was trying to put the brace right at the bottom of the legs, but there was many difficulties here. Moving it up to the space between the first two hexes was much easier to accommodate and easy to adjust to happen on all 3 sizes of the model.