Hi there @Famer,
In the case Assembly Features, especially for Frame members, I would recommend using sketch elements, with a combination of "Project to Sketch" [formerly "Include"] command and manually sketched lines/arcs to dimension from and to....as midpoint will only work for 45 degree miter cuts.
Also, check that the "Keypoints" selection filter, for your dimensions, has the correct setting. I normally just set it to "All"....I really wish this could be set as the DEFAULT.
Design Manager Streetscape Ltd
Solid Edge ST10 [MP3] Classic [x2 seats]
Windows 10 - Quadro P2000
I think you are talking about the "peers" setting in tools. It needs to be on. This is another thing I wish was always on by default.
Peers on/off is the next thing I plan to add to my quick access toolbar in every environment. I frequently have to use peer on for one side of a dimension and peers off for the other side.