Dear Phil,
Thank you for your forum thread.
When copying some wall elements using Ctrl+C and Ribbon> Modify > Clipboard > Paste >Aligned to Selected Levels you have the opportunity to specify the base constraint in the pop-up dialogue box and adjust the top constraint in the properties panel as well before pasting the walls.
I have recorded a short video on this method and uploaded it to Autodesk Screencast - here.
Please, let me know, if I have understood the issue correctly and if the method I have provided has allowed you to resolve the challenge you are facing.
Thanks.
Zsolt Varga
Autodesk Technical Support