I got tired of waiting for Stardock to address this, and after hours of futile research into alternatives, finally just put a period (.) as the first character in all my Fence names. Now all the Fences appear at the top of the Start10 menu. Problem solved. Not a particularly elegant solution, but it works.
Now I notice that there are entries missing from a lot of Fences menu entries ... but that's another day's problem.