A way to do it without having to set it for each one (unless that's what you want to do
) is to add a line at the end of the layout function that looks like this:
self:SetAttribute('initial-scale', 1.2)
That way they're all set as they're created. I'm not sure if SetScale is protected during combat or not, but if so you can run into problems if the unit frames are created during combat (logging in after a DC, for example). Using SetAttribute gets around that.