Thank you for your post.
If I use the menu items in the control bar of the viewer window to send PrtScr to the host computer, I still get the local screen capture instead of triggering the host screen capture.
When you use the "Send key" -> PrintScreen command in the Full Control mode
toolbar you copy the remote screen image to the clipboard on the remote
(Host) computer. The clipboard should automatically sync with your Viewer computer's clipboard and you should be able to paste the image in an image editor on the Viewer computer.
If this command doesn't work please make sure that no other programs are intercepting this key on the remote machine. Sometimes, screentaking applications replace this key's action with their own.