With reference to the following snippet from a previous post:
".....Preview window keeps the size user re-sized to last time.
[Ping] We will consider to support this in next version of SyncToy."
Please go beyond consideration and definitely implement in next version. The position of the preview window on opening is unsatisfactory (at least for me) since the control buttons are out of sight below the bottom of the screen and there is no way to change the default window size/position.