the :SetUserPlaced(false) works as well... you just have to reload after you call it
edit::
also you dont have to uninstall/reinstall.
if the frame isnt in existance when the UI gets reloaded or is closing (logout) then it wont save its position.
So if you disable your addon, reload UI, then enable your addon, the frames saved locations are lost accrodign to your layout-cache.wtf which stores the position of frames between sessions