It's possible to modify the position of the frames after they've been created.
1. Enter the Structural Frame Environment.
2. RMB the Frame you intended to modify, from the Edge Bar.
3. Select Edit from the Shortcut Menu.
4. Click Modify Cross Sections icon from the Ribbon Bar. You'll notice all the Cross Sections of the frames are highlighted.
5. Click Cancel icon from the Ribbon Bar.
6. Select any Cross Section. (You should try with single selection first.)
7. Click Accept icon from the Ribbon Bar.
8. Use the Arrow keys from keyboard to move the Cross Section.
9. Click Finish icon when you're satisfied with the position of the frame.
HTH
Regards
fwc