Hi deanw,
You can do the following operation to make the layer scaling fixed:
1) Open the Plot Details dialog. Choose your child layer (e.g. Layer1) in the
left panel of the dialog, and choose "Display" tab in the right panel.
2) In the "Scale Elements" field group, choose "Fixed Factor" radio button,
and enter "1" as the scaling factor value.
Hope this helps.
--Hideo Fujii
OriginLab